Digimon Rumble Arena 2

Beat him in 1-Player mode

Defeat BlackAgumon in single player mode when he surprise attacks you. He can digivolve into BackGreymon and BlackWarGreymon.

In single player mode, defeat any of the following Digimon to unlock it: Duskmon, Diaboramon, Omnimon, MaloMyotismon, or Neemon.

Just beat the game and/or Character to unlock.

Encountering Kaseidramon is a near-impossible glitch, and not meant to be accessible at all during normal game play. Whenever you encounter a Digimon while moving along in one-player mode, a glitch can occur that confuses the game. The programmers originally designed the game in such a way that if there is any fatal malfunction while entering a fight, instead of freezing the game, it would, as a novelty, automatically transport you to an unbeatable fight with Kaseidramon, who will usually just defeat you with a move or two, then return you to the title screen. Use of this function was removed for some unknown reason, but the fight scenario remains in the game and occasionally a glitch will trigger it. The fight with Kaseidramon is meant to be swift so that you can return to normal game play. A strike with his Zantetsuken sword is usually an instant knock-out. The One-Hit Kill rule cheat does not work on him, and he cannot be unlocked.