This guide will help you kill Mobula (chapter 5 boss) on your own in the most efficient way possible. This is the hardest boss fight in the game by far. It will be very difficult for most people and could require a lot of practice to beat solo, but it's still very possible, especially for Guitar Hero/Rock Band veterans (or any difficult rhythm game). If you are having trouble, you can have a second person help you via Xbox's copilot feature. Have the more skilled person take the most important double kick lane, and the second less skilled person take the snare and cymbal lanes.
This achievement stacks with the following:
Here's the tutorial video, along with the full description from YouTube posted below. Check out the final paragraph for boss specific strategies.
This is a tutorial on the most efficient method to kill Mobula on Extreme difficulty, on the Xbox One. You can obtain the achievement on either Story or Arcade mode. I played on Arcade mode so I could show off the full chart.
First of all, make sure you spend time tweaking the settings. Go into Gameplay and turn on the "No Overheat Mod", and change "Musical Score Speed" to x0.5. The "No Overheat Mod" allows you to spam as much as you want with no penalty outside of losing your streak. Changing the "Musical Score Speed" gives you more time to see the notes, but more importantly, it increases the size of the timing window, making it MUCH easier to keep your streak going. You can still earn any achievement in the game with these mods on.
Next go into Controls and make a custom control scheme. Both default options are terrible in my opinion. Make sure that the up kick and down kick are mapped to separate thumbs, then use the bumpers and triggers for snares and cymbals. I personally chose right on the d-pad for down kick and X for up kick, and then LB and RB for snares and LT and RT for cymbals.
Finally, go into Sound and tweak the Audio/Video Calibration. The Video Calibration test works fairly well. The calibration changes every time you hit RB, so keep hitting RB with the flash until it stays pretty consistent. For me, I landed at -25 MS. The Audio Calibration test is completely broken unfortunately. Thankfully, the game is very good at indicating if you are early/late during gameplay. If you notice that you are consistently late in a song, then increase the audio delay (ex: move it from -50 MS to -70MS), and vice versa if you are consistently early. For me, -220 MS is where I landed eventually (that seems like a crazy high number but it worked for me for some reason).
Now for general boss fighting strategies:
Always focus on the double kick lane first. This is the most important lane by far, because it does the most damage, and anytime you miss a note or hit the button too many times, you lose your streak and go back to the pistol, which causes you to miss out on a lot of damage potential. However, the snare and cymbals don't affect your streak at all. You can spam them, or ignore them, and still maintain your double kick streak. The more you hit the snare and sniper, the more often you will throw grenades and fire sniper shots, so they can be useful if you can manage to hit them. But you never want to hit them if it causes you to lose your double kick streak. The sniper is more important than grenades in boss battles, as it does single targeted spike damage; so focus on that before grenades, if you have to.
A very nice thing about this game is the HUGE timing window. You'll notice that there are 'Perfect', 'Good', and 'OK' timings. These all have different point totals, but they all do the exact same amount of damage against the boss. Which means if you hit the notes anywhere in the massive yellow timing window, you do full damage. You can completely ignore the timing of the songs and just hit the notes whenever they are in the square and still do fine. Use this to your advantage on the fast parts! Instead of alternating back and forth, it might be easier for you to hit both up and down kick at the same time.
Now for this particular boss fight:
Mobula is the hardest boss in the game by far. He has 2 phases, each with quite a bit of health, and is constantly summoning small enemies to be bullet sponges. As soon as you kill the first phase, he disappears for ~15 seconds then reappears in his second phase. You won't get the achievement unless you kill his second phase before the end of the song. On top of that, the chart has many extremely fast patterns with difficult timing. You will need to be very skilled, or practice a lot, to get this one by yourself.
You will need to rely heavily on the sniper in order to do enough damage to this boss, but there are still some points where you can safely leave it out. The details of which lanes I focused on are:
0:15, kick and cymbals (way too hard to hit snares here);
0:40, all lanes (slow and easy, and you need grenades to deal with wolves. You should kill the first phase during this slow part);
1:25, kick and snare (you can probably drop snare here if you want, I included it because it helped me keep track of the rhythm on the fast parts);
3:00, kick and cymbals (lots of fast kicks, but the cymbals only come during the breaks, making them easy to include here);
3:45, all lanes (easy part, might as well get extra damage);
4:28, kick only (constant fast kicks, way too hard to include anything else. In order to keep up with the speed, I use a strategy where I hover my thumbs steady over the kick buttons, then just shake the entire controller back and forth so that the buttons move into my thumbs. When done correctly, it feels very similar to alternate strumming on a Guitar Hero guitar.)