DISCLAIMER: This solution was written for Proud Millionaire and Legendary Devil Hunter, but it contains lots of helpful things relating to S ranking the Bloody Palace.which you most certainly can do if you have S ranked DMD.
When done properly, Proud Millionaire and Legendary Devil Hunter will be the last you get, and won't take much grind if you can comfortably S rank the palace; perhaps 7 hours, and they will be done together. I got them to unlock at the exact same time, after cleared all other achievements, by doing three runs of the Bloody Palace. Four may be needed, if you are a better player than I and S ranked the game with less difficulty. Here are the stats from my runs:
1st: Time taken, 2:35. 3.2.~ million score, 102,000~ Proud Souls.
2nd: Time taken, 2:10 3.8~ million score, 111,000~ Proud Souls.
3rd: Time taken, 1:55. 4.2~ million score, 120,000~ Proud Souls.
All runs done with Automatic Regular Nero. I believe that 3 million points is the cutoff for S ranks, and using a Super character divides your score by 5 and therefore can't be done.
Use the Bloody Palace guides on site for reference to which floors contain what. There are plenty of videos out there to watch that show ways of playing each floor. There are some things I noticed which are great to know, and I will list these now:
This is the most essential idea for success in the Bloody Palace. When monsters are on your screen, they will begin new attacks. When they are not, they won't (the fish swords seem to be something of an exception; you often don't see them until they land on you or pop up from underneath you). Since the arena is circular, you can keep to the edge and focus your camera away while running around the perimeter. You will not use RB targeting much, except when you need to send your charge shot to a specific target in a group of enemies and need to make sure it wasn't wasted (blitz levels, alto angels, clusters of mephistos), so if you are in the habit, try to break it.
Enemies off camera will not begin a new attack, however they will finish one that has already been queued. Even if you don't think an attack has been queued, because sometimes (especially with the angels) there is no actual graphical change at the beginning of it, it is important to keep dodging for a little while after you have pivoted the camera away from everything.
Simple. Keep moving and jumping. Also in this category, I will list the importance of the TOWARD+Y+RB attack. This attack allows you to push an enemy back a long ways, thereby separating it from a crowd, while traveling with it and dealing damage along the way, especially if it is a charged attack.
Use your "i frames"
I frames are bits of your character's animation where he in invincible. Knowing these is one of the most important things about this game, and it's also what gives Nero an advantage over Dante in damage mitigation. Nero's i frames occur during the whole Devil Uppercut that happens when you activate Devil Trigger. 1.5 seconds of pure invulnerability. It is important to note that if you are doing something else when you activate DT, or if you haven't completely finished a previous attack, the uppercut will not happen. It WILL happen if you are being beat on in a combo, say, by Dante or by one of the angels (thus interrupting their attacks), and it will stop your knock-back if you activate it when you have been hit. There are also a few jump i frames at the beginnings of both character's jumps, but Dante has more in this department and dodging this way with Nero is iffy.
Last thing about the devil trigger: It will get you out of a tough situation. Say that asshole frog boss swallowed you and is about to start chewing, or a blitz somehow managed to grab you (i.e. you weren't jumping enough) and is going to 'romance explosion' your face. Popping DT will get you out of these situations, and will also deal damage to nearby enemies and interrupt them. Mastery of the DT is essential.
Level 3 Charge Shots Win You The Game
They really will. When you have isolated one or two enemies for a spanking at the edge of the map, with the camera pointed away, still fire your charge shots blindly off screen by pressing that direction on the stick and just firing. There are a few instances where you will want to save them for specific crowd control (blitz levels) but other than that, it's a great way to deal with almost anything and bring down Mephistos and Fausts from the sky. I found it extremely useful when having to juggle 2 or more frosts. A charge shot keeps one off your back for a good 6-8 seconds, and interrupts any bullshit they might be thinking about doing. They are also the only way to handle Blitz, which I will go into.
Get used to MAX-act
I bound this to right trigger and gun to left (and taunt to X), but it may be better reversing the two for most people. You do a LOT more damage (and to more enemies at once), create some i frames for yourself, cover more ground, and get more style points when you use level 3 revved attacks, especially the TOWARD+RB+Y and the AWAY+RB+Y attacks. The timing widow is tight, but worth getting good at. It exists at the point right after your attack lands (not after you push the Y button; make sure you pay attention to what Nero is actually doing or you will wind up spamming out of sync with his swings).
Levels to think about
30, 38: Both 'Blitz accompanied by other shit' levels, I nearly died on both of these my first time through, mainly because other enemies around really distract from the RB targeting system, and I wasn't landing my charge shots on the blitz very well. You really can't handle a blitz with shield raptors or mephistos around, so drop his shield (or don't if you're good) and take them down, then go round two with him alone.
65, 92, 99: These levels all have Alto Angels with a specific programming that is interesting: They will send their bianco angels on kamikaze missions destroying them until there are non (or just one) left. If there is one left, you will have to kill it; the altos only issue orders to two or more. That said, don't attack. Just let them kill themselves off.
67: How annoying. A Blitz accompanied by two altos. Probably the best and safest strategy for this (thought it's not exactly what I do) is you wait for your charge shot, make sure it lands on the blitz, and do your best to get his shield down right at or slightly after the time when the altos appear. This gives you good amount of time to hopefully take one down, or severely damage both. At that point, lvl 3 charges from off-screen will finish them/keep them occupied while you take the Blitz' shield down a 2nd time (see Blitz strategy).
85: Hardest level in the tower. Two simultaneous Blitzes. I have never failed the tower, but both times I almost did, it was on this level (well once I was down to 2 bars on Dante). Your goal here is to make the first blitz turn red. If you can land all 3 combos (see blitz strategy), aweoms; you got lucky. If you can't, deplete his health as much as possible. It's enough to make him change colors; once he does, he's as good as dead, though it takes some time and you will have to dodge until it explodes. DO NOT LET IT GRAB YOU AT THIS POINT. If it does, DT. If you don't have DT available, it's game over. Use the camera trick, make sure your lvl 3 charge shots land, and keep jumping like a Jack Russell on PCP.
Any level with Chimerae: Ugh. God. I hate the freaking Chimera. Don't use your buster on them, just lvl 3 charge shot and zoom in for some stabs when their blades aren't flailing. Speaking of Chimera...
Chimera seeds = free health: Save them for last on a floor, unless they're being dicks and pouncing at you too much.
Flying swords = free magic: They often give health as well. Also, they are weakened when spinning and readying to attack you, so often any level charge shot at them during this will break them, and it will always halt the attack.
Big Fat Freddy Kruger Scarecrows = Utterly benign, if you keep them off camera. Very dangerous on the last 20 floors if not kept off camera. Always save them for last, and keep them out of sight. The only exception to this is that when they devil trigger, they have a MASSIVE amount of health and take forever to kill. To prevent this, point your off screen lvl 3 shots in their direction, whittling them down before they start to berserk.
Dogs: Tortured-Man's-Soul-in-Hell's best friend, and goddamned annoying. Don't Buster (demon arm) these. The animation takes forever, and the Doggie Cannon rarely hits anything. If you have lots of enemies below you, Devil Trigger, jump up and buster one grab it by the bollocks (bollocks, literally, are the 'dog's balls'), and squeeze. The ensuing air-to-ground cannon is quite useful, and afterward the doggie is discarded with appropriate and satisfying disdain.
Fish: As annoying as the dogs, a lvl 3 shot will pop them out of the ground, and any other type of shot will slow them down for a second so you can snatch them up with the buster. when they were about to land on me, I generally made a habit of using my DT defensively to knock them out of the air on their way down, and then proceeded to extract their insides.
Alto angels: break their shields with 3 close range uppercuts from the Buster (do this when they're not about to charge) followed by a small leap to avoid their counter. This gives you lots of extra style points and makes them easy to grab (the grab can be interrupted by other enemies, however the somersaults will do damage to anything close). It's always good to use your charge shots on these if they're around, as they have lots of health and they can hurt.
Normal angels: The only thing worth mentioning here is: don't buster them if you've got something else near you. The animation takes a while and leaves you vulnerable. Break shields for style points with two close range Buster uppercuts. These are one of the enemies I mentioned earlier that might be charging an attack without you being any the wiser, and can surprise you from off screen.
Shield raptors, or Assault: These things can be tricky in groups, and I find their chimera form to be more annoying than almost anything else. Don't buster either form of these. The chimera will probably hit you, because the animation takes forever and doesn't significantly hit the things around you. The normal form will just waste your time. I find it best to charge shot, DT, and use TOWARD+Y+RB attack (preferably revved) to bugger the whole lot.
Frost: Annoying unless you use your lvl 3 charge shot to keep the one at bay that you are not attacking. If you accidentally shoot the one you are attacking, go switch targets. Don't let them encase themselves in ice; they will heal. This means, don't leave one alone if it's almost dead. I find the buster attack here to be useful itself for crowd control, because your swing it around and hit a rather large area with it, then you can aim the throw at whatever else you like by pressing in that direction. Use it with care however, because it leaves you open to attack for a bit. As the difficulty in the tower increases, these will begin to dodge your buster an annoying amount of the time. Best to jump in the air and 'air buster' them in later stages. Don't keep these on camera and at a distance, or they will shoot at you with projectiles that are very hard to avoid.
Faust: Can be really F***ing annoying. On levels 80-100, they use their multi-sword B.S. attacks, where they are invulnerable to your snatching them out of the sky. If you see them start to do this and have a lvl 3 shot ready, use it. Hopefully it interrupts. One important thing to note is that if they are 'Buster snatched' out of the air from high up and fall a longer distance, they will not land, rather they will just spring back into the air. Don't let them fall a long way, and keep them as close to the ground as you can when you're bringing one down. The fasted way to dispatch of these (and it's important to be fast) is, once it is on the ground, walk up next to it and DT; the uppercut should happen, and knock it into the air. IMMEDIATELY execute TOWARD+RB+Y+B (pressed all together) from DT form. This attack takes a long time to charge, so use it only when you can. This should kill it or bring it near death. If it's not dead, charge shot it once.
Blitz: Either the easiest or hardest enemy to deal with, depending on whether or not you know this simple strategy. You should be used to their patterns by now, so wait for them to appear to do an attack that will keep them 'present' on screen for a few second, then charge shot them. It usually takes two (sometimes 3; they are immune to the explosion if they are teleporting around I think) to knock their shield down. As soon as it is gone, run up to it and DT. Keeping its back to the closest edge of the map, do a close range buster 3 times. You will unleash flurries that damage it to near death (it can't be killed until it's turned red). During these combo sequences, spam the shoot button to chuck ethereal swords at it during the combo. This won't use up your charge shot. Once three combos are done, he will invariably turn red (you will see a glitch in his animation when he shifts phases. He can be killed after this glitch.). Shoot his with your charged shot and that will killed him and net you an instant SSS combo. Rarely, it won't kill. In these instances, just dodge more and give it one more charged shot to finish it.
A Few Interesting Things About Bosses
First boss, lvl 20: It's worth saving up full DT here, because you will want to use it defensively. Begin the fight by circling the outer edge of the map at a good clip, and put 2 or 3 lvl 3 charge shots in him. He won't do much at this point. It's worthwhile now to run up, hop up to his face, and start wailing away, using DT (and then cancelling it again) when he swings at you, You can also DT through the large explosion he does. If you can't, run straight away ASAP, while jumping, and if you acted fast enough you will escape the blast. His flames should go out, in which case, DT and buster his face off. Once that's done he will be crumpled in a satisfying demon-heap. Charge shot, then Buster him again. He will then reignite, and be more aggressive. Keep charge shotting him, as this will provide you with most of your damage to him now. When you see him punch the ground, run to the right or left in a straight line until you've seen for flame geysers. When he charges (he rears back and his flames burn brighter), get ready to DT, roll away and jump (RB+Left or Right+A) or, if your timing rules, buster uppercut (bustercut?) him and deflect (you have to time this early. He deals his damage to you in this charge before his animation reaches you. Think of pressing B when he's at the half way point to you). This fight shouldn't take long.
Frog boss, level 40: Disgusting. Keep to his side (if he does manage to eat you, DT out of his mouth) and swing away when he's near you. If you attack from the front, you can stun him and then buster your way into his ugly face, but I prefer to just smack him from the side. Always be charge shotting. When his little slag-on-a-ropes come down, you have a brief second for a free buster on them. Just stay in the air and keep spamming it; your first grab will be a free quickie. After that, they will be dodgey. Just keep jumping and double jumping and strafing, and once you have 3 hits he'll try to eat you again. Easy boss.
Echidna boss, level 60: This one annoys me a bit, because she spends more time in the ground sprouting up stalks under you than in previous versions. Just mitigate damage and learn her cues. When she's soaring around far away from you, keep her locked on with RB and as she approaches you for a bit, charge shot her face. You get lots of style points, and it puts her right back in the kitchen. I like to get up in her face and use DT to i frame through her double hair swipes, which she does both above ground and below, if you are close. When she spreads her legs and shows you her dingle berry, you get some freebies. Hop up to the dingle berry and DT. Start swinging, without pushing forward on the control stick, to make sure you stay in the air. The dingle berry will pulsate 3 times, and give birth the first time (a sentence no one has ever penned, I'm sure). On or around the 3rd pulsation, Buster her for a free combo. When she gets to 4 health bars, she enrages and turns yellow. She's more aggressive now, so just be a bit more defensive, using your DT as needed to mitigate damage, and charge shot her for the win.
Credo, level 80: This boss can own you quickly if you aren't comfortable with his attack pattern. The best thing to do is take him down slowly with charge shots and by being in his face all the time. Don't give him distance (unavoidable if he teleports). The way to do this is by inciting his counterattacks and then bustering him. Go up and buster. He will block, then counter with 2 or 3, rarely 4 swings. Just keep jumping right as he starts attacking and dodge. Then buster him for a hit. Rinse, repeat. You'll notice his shield glowing throughout this process. There will come a point where it abruptly stops glowing. DT and buster for a combo. Once he's down to 3 or 4 bars, he becomes a LOT more aggressive, and where he did one semi circle swing he will now be doing two. He also gains a VERY fast straight forward lunge, which you can roll out of the way of (you have to time it early through as soon as he rears back to thrust, usually far away. This is often preceded by a teleport). Just keep waiting for him to finish his attack set and bustering when he does. When he surrounds you with swords, but can DT them away, though it's easy to just jump at the right time and avoid them though. Simple enough.
Agnus, level 100: very easy boss if you do it right. Make sure that you have full health and DT (See level 99 strategy), which you should if you did the previous level properly. Every time I've done this boss in BP, he started by spawning swords rather than dogs, and spawned swords for the majority of the battle if I took care of them fast. Wait till he does, then jump up next to both him and the, DT and hit them all together. This should wipe out the swords, and they all drop magic orbs, replenishing your DT. Rinse, repeat. When he goes down, it's very obvious. Charge shot, then buster. Once this is over, DO NOT LET HIM EXECUTE HIS GREENISH CHARGE ATTACK THING, which he flies to the middle of the room to do. This can be countered by hitting him a few times, or by popping up next to him and DTing, or by a lvl 3 shot. Very easy boss.
Dante, level 101: If you try to fight Dante and not be cheap, he's a right c*nt. So be cheap. He uses lucifer, pandora, and all his styles in this fight. Once he used pandora's TOWARD+B Gunslinger attack on me and nearly got me; it took more than a quarter of my life away. So don't give him the chance. Stay within grabbing range of him and buster. If you're at the right range, he will roll to the side and ALWAYS follow this with a stinger. It can be caught with the buster, but I'm not great at that, so i always hopped over and grabbed again. I usually got him. Keep your volume up and listen to the vocal cues. I'm pretty sure that if nothing is said, then he's going to win the duel, so get ready to dodge. If Nero says "That's all you got?" then get ready to start swinging. Charge shots are hard to hit him with, but they do a LOT of damage, and the ensuing explosion opens him up to be grabbed and bustered. I liked to air buster him. They don't always work, but this way, you don't have to worry about losing the duel, and the attack which he might hit you with is quite weak. It also gives you two spots to use your charge shot. If he breaks free of your grab, he will do a downward slash. You can shoot him right at the beginning of almost every move and connect, and this is a good time to do so. If the grab does land and you manage to throw him to the ground, shoot immediately as he lands. Don't try to get fancy. If he starts laying into you with one of his devastating melee combos, DT immediately when the first few punches land (always conserve your DT and use it defensively on this fight). This should be the end of the story.
I hope you enjoyed the novella guide, and that it proves useful. As always, leave me any criticisms or useful information in the comments before voting negative, and I will alter the solution accordingly.