Bite marks never disappear? Meaning a curse that transcends any divine purification or healing, or regenerative abilities of demon lords? Hell, if it fights an enemy with multiple forms, will it lock them into forever persisting in a single form?! Or maybe only seal the part they bit?
Either way, OP slime, they should be collecting them to throw at dragons, golems, demon lords, and other high-defensive enemies or ones likely to regenerate well. Particularly enemies that have high defensive abilities through being elastic, will consider this slime their bane (unable to even have the bit part "bounce" back). And with how every material is at least slightly elastic, this means it can never deal 0 damage. Your soldiers are too weak to damage the demon lord and its elites? Just pelter it with those slimes, and every bite is a permanent reduction in hp, no matter how weak.