So my final mission squad was sniper/spec/gren/ranger/2x psi ops. I only had 1 medkit on my specialist(3 uses). I had to use one for poison, 1 for hit soldier, and another usage for my grenadier who set himself on fire using his cover shreding skill on the fence in front of him. I had no healing left minus the ability to soulfire a few hp on my psi ops.
I had a one of the metal acid suit dudes mind controlled permanently, he had about 8hp left entering the final room. One of my psi ops was down about 5hp, I was looking to life leach it up. So to begin with I assume the final room is the same due to mechanics. I had 3 of my troops up against the big wall right in the middle, 3 more on the marble shit just by the giant wall. So I was all ready skills cooled down. I moved my mind controlled dude out into the room. Avatar + 2 Archons activate. The avatar moves into a really shit low ground cover hard to shoot position. I end up mind controlling one of the archons, but that's the only usage I have. I also expose my sniper to shoot before ending my turn. I leave my specialist and my low life psi ops in the back and I believe I just decided to overwatch my grenadier. Well then very bad shit happened.
So the avatar uses its giant shitstorm skill and it hits every single soldier I have. I've never seen this skill before, but apparently I have that skill, but I didn't use it due to the fact it read as if it didn't do initial damage so I never tested it. No one dies, my psi ops has 2 hp left. Everyone takes damage, I didn't think my troops were that clustered, and I found out wrong. Turn 2 I was forced to split my units up in two directions because the giant explosive cloud persisted over the entire position I was in. My specialist and grenadier had to go left in some shitty half cover, my sniper ends up in the bottom right corner in half cover, Commader unit ends up behind the first raised platform in full cover. My ranger ends up on the far right wall in full cover. My full life Psi ops also is on the right side but only in half cover. My sniper is shot by the Archon and has 1 hp remaining in the corner.
I use my mind controlled Archon to melee the Avatar. It takes 3 damage, and it fucking teleports away onto one of the platforms to a high ground position in full cover. At this point I feel like I have lost the game. 3 Chrysallids warped in on the right side, the left side had 3 vipers, but they had yet to agro anyone on turn 2. I run my Mind controlled unit up the right pathway right next to all the teleporter ramps to body block/tank (I hope) the Chryssalid agro to delay them getting to my troops. (He ended up surviving 2 attacks with 1 hp remaining)
Because I'm about to get fucked, and I just got owned by the Avatar super nuke. I carefully place my own super nuke so it hits all the units currently visible on the right side, including the Avatar #1. It kills nothing, hurts a lot of shit. I have to take a 68% shotgun shot at a 2hp Chryssalid to try and get my ranger the immunity to damage buff so he will not die, it hits.
The next enemy turn the second avatar, a mech and 2 more units I can't recall + vipers warp in on the right. At this point I just pray they all just walk from the 3rd platform into my giagantic explosive fuck you skill because if they do not, I'm pretty sure I'm dead. The enemy movement happens, no one dies somehow, and like I planned it all along, at least 7 enemy units maybe more were inside the explosive circle the round after I cast it. The second Avatar cast his shit on me circle - this time it only hit 2 soliders + my mind controlled worthless Archon. At the end of the turn I actually feel like I have a managable amount of enemies and can finally do some avatar damage.
This feeling is short lived as 3 muton warp in on right platform 1, and 3 codex on right platform 2. I used a few psi nuke cooldowns to kill the first avatar, namely the lances to make sure it happened but he teleported all the way to the left side, where my injured psi ops, specialist and grenadier managed to deal with 3 vipers, 3 faceless, and last hitting the 1st avatar. I felt really desperate after these warp ins, I decided that I would run and gun up the right side with my ranger, and go for a point blank double shotgun blast on Avatar 2, hoping it would be left low enough that my sniper could finish it off. Well, magic happened and my superior laser sight came through. Double Crit, 15 and 14? either way it was enough to outright kill the 2nd avatar. A fucking miracle with only just my ranger. Using skill shenanigans I slogged my way through the enemies on my right.
3rd Avatar + 2 berserkers + 2 muton spawn on the 3rd platform in the left - I have at least 1-2 turns before they show up. Right side spawns a gatekeeper and 2 more archons. I end up lining up a double null lance on the archons, and mind control on the commander came off cooldown just in time to snatch the gatekeeper. The gatekeeper nuke helps me finish 2 of the Codex off + raises me 1 psi zombie out of Avatar 2.
I can't remember exactly how many turns pass, but it was barely enough to get run and gun back up when the 3rd avatar climbed the ladder of the central platform. I end up shifting my gren/spec/psi ops back towoards the right behind the giant wall because I know there is only 1 avatar left. I don't think I can deal with the berserker's and mutons when they arrive. Its too much health and I'm out of options. I call on the power of my ranger, with run and gun, he can barely make the platform to try another point blank execution. The first shot - its a CRIT holy shit. The second shot is a GRAZE of just 4 damage. The Avatar teleports to a low ground position. My turn ends. The avatar decides to mind control my ranger. I lose vision and he is coming to kill me. The next turn the AI decides to super nuke my gatekeeper+psi zombie as I have kept my soldiers far apart as I can manage. The zombie is also missed by my mind controlled ranger and at least 2 other units. However, my ranger is now standing mind controlled inside the explosive zone of death. He begins to bleed out as the explosion puts him down - but I do not have to kill him myself.
I managed to juggle my cycling psi nukes, some sniper shots, my last combat protocol, and 1 82% grenadier shot on the teleporting third avatar to finish the mission. 1 soldier bleeding out, my sniper at 1 hp, my specialist had 4, one psi ops at 2.
I was so relieved I didn't fucking die on the final mission, game was really great.