Most powerful character would have to be scholarsage with meteor, after you get the shermantree wand. Just run up to any group, unload meteor, have your Paladin hold the line, have a healer as back up, and easy-breezy.
I have all but the Top Left achievement. One can be obtained by going through the cave, picking up the item and turning back. Another can be obtained by taking that object to your ship. A third may be obtained by hopping onto your ship then into the crevice on the left. A fourth may happen if drop into the hole when the hot stuff isn't coming up through. A fifth may occur when you reach the top of the mountain drop through the hole.
I think you may want to reconsider calling them Champions of Chaos. It's the same as calling them Chaos' Champions. It would be better to call them Champions of Order or Champions over Chaos.
I'd suggest saving all of your bullets unless you have survivors with you. You can easily run up to them and toss them till they die. You can easily dodge their attacks to get in close.
I cannot stand the Lorry mission with the capsule. It's difficulty is insane compared to everything else. You can't drive fast enough, the ropes holding it break even before you drive it, and if you try to go on ahead, it gets killed anyway.
The best way to handle Hypergenezus is to use Colonel Stuns in all but the boss row. In the boss row upgrade them up to 3 CHIEF stuns, use time stop when he summons the kamikaze zombies and you'll kill him before he fires his missiles.
While the nerf was a nice idea as Kraken was OVERKILL. It lessened the constant grinding to the point where it was enjoyable again. I could go after insanely tough bosses with less worrisome behavior. The grinding isn't so bad as the 55 areas to get to the boss to reap your reward is.
You need to recruit your allies from the FRIENDS section. There you can find characters to level the playing field. Some of you out there have over 700 damage and you're not even level 20. I recently recruited a character with 1402 damage (or something like that). He has been making this less of a grind.
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But they are the champions of chaos! :D Thanks for the feedback !