For all classes: The trick is to throw a bomb at one of the wooden blockades on subterranean fortress route A (credit: mymarou). I was able to hit 110k on it and these were my (important) stats:
Fighter
LVL: 98
Sword: 190-254, LVL 98, DMG to objects + 29%, STR + 28
Shield: Damage dealt +19%
Amulet: At low HP, DMG dealt + 25%
Gauntlet: When LP is 0, DMG dealt +24%
Belt: Damage dealt +16%
Don't forget to use a strength draught before throwing it, and let your LP go down to 0 and HP to LOW (you can tell its low when the unfilled part of the HP bar is flashing red). Also you must do this on infernal difficulty.
Good luck!
