He is so weak against elemental magic that he takes 250 times more damage from fire, ice and bolt. However, since Trimag is actually all 3 elements combined together, this means that the spell does 250*250*250 times more damage to him.
This also means that when he uses magic, he does 250 times less damage, so the only thing his extremely high LV makes him do is attack incredibly fast (about 5 times per turn)
But now you can see why it's hard to port one of my RPGs to a language that lacks good floating point support.
Even with 32 bit integers this boss would overflow.