This is my no-skull Legendary walkthrough for this mission. If you use easier skulls or an easier difficulty, you will get this MUCH easier, but I was going for the true experience on my first run through without any skulls.
Update--I just played this mission for fun, and decided to try to take out the Banished Base. I failed to the Banished capturing all the points, but I think I could've easily done it using Kodiaks and Spartan's to take out the Banished base, and making sure to recapture/defend the 3 domination points.
I failed at least 3 times before succeeding originally--this was the hardest mission for me by far!I'll be going step by step below, but a few things I did not realize at first:
1. The first fail was caused by not having enough anti-Air when the Forerunner supership attacked.
2. The 2nd fail was caused because I didn't realize I could actually get 2 bases!
3. The 3rd fail was caused by not getting the right troops to the right capture points quick enough.The mission goals first:
1. You must build enough anti-air to knock out the Reclaimer superweapon/ship that will attack soon after you knock out the initial Banished attack.
2. You must rescue the 2nd base as soon as possible.
3. You must build some artillery and snipers to support your point capturing and defense.
4. You need to build a fleet of roving Hornets and Nightingales to support infantry capturing other points.
5. STAY AWAY FROM THE RECLAIMER. It kills the Banished , no need to attack it, and it won't attack your base after the first time! It just flies around the map, generally going between points A and B and the middle of the map. Make sure to hide your units though when it approaches a capture point you are controlling!Step by step mission walkthrough:
1. Immediately after the mission starts, select all your units, and bring them in front of your base. Then build a supply pad and an energy extractor. You want to build up to 4-5 Wolverines RIGHT NOW. Also, use your Spartans to hijack Wraiths if possible during this initial attack. You will be able to weather this first attack pretty easily if you keep your units in the back and use your Spartans slightly in front. Also build two Turrets on the front of your base(BEFORE the Wolverines) and upgrade them to Anti-Air!
2. After the initial attack, there will be a cutscene, then you will be attacked by the Reclaimer. Spread out your Wolverines and Spartans so they don't all get downed immediately, and make sure to watch out for the special attack--when it looks like a spotlight on the ground, get your units out of the spotlight! You should be able to take down the Reclaimer first try this way.
3. With the Reclaimer down, focus back on your base. Make sure to upgrade ALL your resource buildings for the rest of the mission as soon as possible, both Supply Pads and Energy Extractors.
4. Now, build at least 2 Snipers, send one to provide overwatch for one of your Spartans, and send one of your Spartans North. You'll find a remote Energy capture device to capture. Capture it with your Spartan, have the Sniper positioned to the East in the hills, and leave the Spartan and Sniper there for the rest of the game! They were able to handle all attacks and were a very useful Banished distraction. Put the other Sniper in the Garrison point right by your base.
5. Around the same time as #4, gather up the resources behind your base with a spare unit, and start building 3-4 Kodiaks. You will want to position them below your base, behind the Garrison point, as they can then fire from there and cover nearly every Banished attack on your base, the Garrison point just to the West of your base, AND the Domination point A below your base! Also, very important, build 2 Artillery Turrets on the back of your base. You could even consider getting rid of BOTH front Turrets and putting 4 Artillery Turrets on your Base. The more long-range attacking ability you have the better!
6. Sometime around now, Alpha Base will complain they are getting attacked. Use your ODST drop near the Wraiths in front of Alpha Base, and have them grenade the Wraiths. You have to eliminate all Banished troops around Alpha Base in order to gain control of it, so use your ODST's and possibly some backup from your main base(It works to briefly send a couple Spartans there before your send them to Point A), and have your troops around Alpha Base mop up. There will be an annoying Reaver that jumps away when it's on low health. Hunt it down, and kill it. If you don't gain control of Alpha Base right away, go North from Alpha Base and there will probably be a Banished squad hanging out near the Banished mini-base. Take out the random Banished units, and you'll gain Alpha Base!
7. Immediately start building up on Alpha base--your goal overall is to have 2 Foundries(one on each base), 3 Airpads(2 Alpha Base, 1 Main base), 1 Armory(on the main base), 1 Barracks(main base), then 4 Supply Pads and 3 Energy Extractors, until you have enough energy for all important upgrades, then get another Supply Pad.
8. Important Upgrades, in general order of importance: Supply Pad/Energy Extractor Upgrades! Barracks Upgrades!(the overall infantry improvement upgrades to help your Spartans and other ground forces) All Airpad Upgrades! Armory Improvements(especially the Base improvement upgrades for stronger turrets!). Base Upgrades(to get T3 upgrades). Foundry Upgrades last, but very important to strengthen your Kodiaks damage. Optionally, you can also level up the Snipers so they do more damage, which can be quite helpful.
Also, through the mission, for leader power upgrades, make sure to upgrade the Turret drop, healing power, and veterancy upgrades first, then the archer missile strike.
9. At this point you should have a fairly stable setup, and be building up quickly. The Banished WILL attack you once in a while with a roving force of troops. however, with Garrisoned Snipers to spot them, and Kodiaks to wreck them, they usually run away as soon as they are almost wrecked.First part down! Now on to the gritty stuff.
10. Send your 2 Spartans not guarding the Energy Extractor to Point A south of your Base. The Banished might have this captured already, and will probably have a turret defending. Make sure you have plenty of attack force(I usually called in a turret drop AND ODST's, and micro-managed my Spartans jumps to hit the Banished force the best). The first time you go here, there will most likely be a Brute Warlord! Your turret will rip him to shreds, so possible send in your Spartans, then drop the turret, and ODST's, and focus fire on the Warlord. If you have your 3-4 Kodiaks in position, you'll be golden.
Throughout the mission, the Banished will attack this point. You will have to keep an eye on it, and I simply left the Spartans there and dropped a Turret everytime it got attacked. Eventually your Spartans might even get wiped out, so sometimes an ODST drop will be super helpful and even better, a Heal Power!!
11. Once you have Point A, focus on building your roving Hornet/Nightingale army from Alpha Base. Once you have at least 4 Hornets and a couple Nightingales, you should be able to take Point B. Try to have a Turret drop available though for the first time as there will probably be a Warlord waiting. A Turret drop, ODST's, and Archer Missile strike should work wonders taking out Point B.
12. With Point B captured, park 1-2 Kodiaks behind the hill to the North of Point B so the Reclaimer and Banished won't find them, then build up your Hornet army to assault Point C. It's also helpful to put 1-2 Snipers way in the back behind Point B where they can just snipe away at the Banished reinforcements along with the Kodiaks.
13. Don't forget to keep an eye on your main base, making sure you still have Snipers in the two Garrisons nearby, the Kodiaks below your base are alive and well, and your Spartans at Point A are surviving!!
14. The Banished WILL repeatedly use the very annoying glassing beam and target your Hornet army. And WILL be successful at killing most of it every time. Be ready to spam Hornets and Nightingales repeatedly! Try to max your army with Hornets and Nightingale's and a few ground troops to capture the points. The Banished will also repeatedly use the Troop Drop ship Leader Power to try to recapture the base points. However, with a Hornet army, you can wipe them out really quickly as very few of the Banished units used are anti-air!
15. Once you have Point B comfortably captured, with snipers and Kodiaks positioned behind it, and a nice Hornet/Nightingale army(10+), move towards Point C. It will be really easy to capture, and I highly recommend putting an ODST troop into each of the Garrison points here! For some reason, the Reclaimer did not kill my troops in the garrisons, and the Banished ran away from them really fast!
16. After capturing Point C, move further to the west edge of the map, up the hill, and take out the Banished mini-base here, put some ODST's in the Garrison, and try to get your rescued UNSC troops back to safety if possible.
17. You've now reached a fairly stable point. You should have all 3 capture points, and now can just respond to Banished attacks on Points B and C with your Roving Hornet Army, Turret drops, and ODST drops. You could consider building a few Scorpions to help support Points A and B, and also more snipers to help out your Spartans on Point A.
18. Make sure to keep your Hornet army alive and reinforced, your Kodiak's alive and well, and your Spartans alive and angry.. oh yes, your ODST alive and ... chipper.
19. The hard part is done! I did not bother trying to do the bonus objectives to rescue the troops or take out the Banished base on Legendary as the Banished won several times because I simply let them get too many capture points. I instead focused on building up then the capture points and won easily finally.
This was super long! Sorry about the wall of text, but it was a really hard mission on Legendary, and not very forgiving.