Which new units did you like in World of Xeen?

I'm reading this and realizing that I haven't seen more than half of the creatures being discussed, even though I've encountered all sorts of messengers (of peace, war, etc.: 2000 hit points each and they don't attack anyone on the battlefield) and griffins (and, it seems, on the same map). But what are these nightmares, sorceresses, metamorphs, and Santa Gremlyns? Please explain it to me, I'm a bit slow...