Final fantasy 8 riddles

[BG-57]

If memory serves, the unpollutable blood line refers to it being immune to poison. Here's a list of monsters (eliminating the incorrect guesses) that have immunity or absorb poison:

BGH251F2, Blue Dragon, Cocatrice, Elvoret, Forbidden, Gerogero, GIM47N, Hexadragon, Iguion, Iron Giant, Omega Weapon, Tri-Face, X-ATM092.

I'll guess Iron Giant, since that sounds like a locomotive.