I some how trigered a bug that gave Derek 15'999 in HP and made him super strong (I just lose a few HP even when fighting over 200 jerks). Thanks to that, I just completed the first endless dungeon.
Haha! Well done!
It's a bug, but also not a bug ;) It's fixed now.. But your Derek has gone nuclear now. You can upgrade him to make him normal again.. Or you can beat EVERYTHING!