attack upgrade kind of makes this game easy, considering that every time you attack you effectively generate 5 guys. As long as you don't screw yourself during shields phase it's pretty hard to lose.
My FOO strategy for winning any fight is to pick Medic and just block, shooting between attacks. His ranged attack is almost immediate, no wind up time. I once beat 5 enemies at a time like that!
Erica seems a little OP compared to everyone else. Her passive is by far the best, and though her special power is great during the stage and not so good against bosses, I felt like I really couldn't have anyone else as team leader because her passive was just too important. The others have nice passives and skills, but Erica is simultaneously your tank (with the most HP), your single target DPS, a good AoE clearer, your best last ditch effort, and an awesome regen bot due to the potion drop buff. That's maybe too many things?
I was so disappointed that it didn't seem to be efficient to stack buffs/aoe and win but I was pleasantly surprised! Multiplicative damage plus lots of AoE stunning is really cool and fun to play.
While killing the dragon I made the mistake of putting one of my heroes on Counter while my Might Potioned Dash swung at the dragon. What basically happened was he hit the Dragon into Barbara, making her take 18 damage and letting her counter, and the counter made the dragon rebound off Dash, making him take 20~ damage, and then it just repeated like 8 times with Dash Barbara and the Dragon duking it out. It was a fun moment until I realized that basically what it ended up to doing was leaving the dragon at half health while I lost both of my characters.
It feels like the game should reward you for having those moments where you land several counters off at max Force in a row, instead of letting the dragon hit full damage on your characters 8 times in a row for minimal gain...
I love the game though, innovative battle and a great amount of polish to it.
If you want to clear all the challenges really quickly here's a good deck:
5 Solarian Archer
5 Solarian Windblade
4 Ward of Light
3 Blessed Day
Just stay generally on 3W power and vomit out archers and windblades. Blessed Day speeds up your win a little, Wards of Light are for massive things. For On The Brink just replace the Wards of Light with Bandages so you don't die to a random unblockable bot.
The trick I find once you've gotten all the upgrades is to keep finding ammo, and for some reason shooting while you're on fire gives you a tremendous boost in speed.