Corruption

Each enemy in the game has a chance to be corrupted, similar to Adventure Story [go check that wiki out]

Corruptions will boost stats for certain enemies, making then harder to fight.

At corruption 1 [Level 4+ then the enemy's level]

HP +5 Power +2 Defense +1 SP +1/2

At corruption 2 [Level 6+ then the enemy's level]

HP +10 Power +4 Defense +2 SP +2/4

Finally, at corruption 3 [Level 11+ then the enemy's level]

HP +20 Power +8 Defense +4 SP +5/10

These stats will be boosted by a bit depending on what world you are at. What else does corruption do? You might ask. Well, it gives enemies new gear drops, as well as a +4% more chance to get cards. [+8% if C2, and +14% if C3]