If you follow the anime, the first movie of digimon, Diaboromon is the first bad guy in dark side and he is very strong. He is finally destroyed by Omegamon (Omnimon). His strength is he can create another copy of himself whenever he attacks, so there is many Diaboromon is created and only Omnimon can destroy them all at once. Come back to the digimon card game, [BT2-082] Diaboromon, his effect is: When attacking: you may play a "Diaboromon" Token (LV6, 14 cost, 3000DP) without playing its cost. So if you let him stay alive in the battle, the longer he is, the more Diaboromon he creates. The disadvantage for Diaboromon deck is: You can not digivolve this LV6 Diaboromon to any LV7 digimon, so it is ending here. Diaboromon is a white digimon, it is not purple or black to digivolve up-to Millenniumon.