Serious question from my game on Sunday.
Can you make a troll into a zombie?
Here is the problem:
Zombie requires a "relatively complete dead body" and takes 1 minute to cast. So far, so good.
A DFM1 troll has Unkillable 3, with an Achilles' Heel of corrosion or fire damage.
Now, it depends on how you rule, here.
If you rule that any remaining little bit of a troll will grow a mouth and become a new troll, the only was to finish one off completely is to totally reduce it to jelly with acid or burn it to ashes.
If you rule that all you need to do is short-circuit Unkillable with a death blow (even a point or two) of corrosion or fire damage, then you can end up with a "relatively complete dead body."
I rule the former - you need to destroy a troll utterly to keep it from coming back. It's vastly creepier that way and emphasizes that "nature" doesn't play by the same rules in fantasy gaming. Trolls are mundane creatures, except they are like athlete's foot - leave a little, end up with a lot.
But is there a way around this?
One suggestion one of my players had was that if you take a troll to -10xHP, it's "dead" until it heals. Keep it there with constant chopping up of the corpse. Your friend casts Zombie on it while it is still technically dead. Bang, zombie troll.
The flaw in this one is of course that Unkillable means you don't die - so you are never a dead body. Even if you are a body, you're not dead.
So in my games this is impossible. Funny, but impossible.
You can inflict undead status that doesn't require death (ring or armor wraith, vampire), or have trolls come back as undead post-destruction (ghosts, spectres, etc.), or are self-inflicted on a living thing (lich.)
So technically, the "horde of vampire lich-trolls" I used to threaten the PCs with in my old game is possible. So are ghost trolls, wraith trolls, spectre trolls, and maybe even shadow trolls. But no zombies.