According to the Wisdom Tree, he "likes to hide in dark places", guess that means a night level.
In the Almanach, he's in the 4th row, # 5.
4-10, during the "lightning" level, from what others are saying, playing through again now to see. Make sure to have something to blow the fog away so you don't miss it.
Once again snatching defeat,
From the jaws of victory.
There's no fog in level 4-10. Anyways, you can't miss him, since he appears along the others in the zombie preview, and you'll have to trouble beating him since he appears when you're fully armed.
It seems beating him there unlocks him in other stages, because he just popped in my Survival Endless game.
*you'll have no trouble beating him
Ah ok, I haven't started another story mode yet.
Yeah, saw him in the preview. He died at the far right, I never saw what he did. He yielded 4 diamonds though.
Does he for sure need to come out of the Zomboni tracks?
"All you've got is an unconfusing name. You can't compete with a guy who crushes planets." - GoodApolloIV
There are no Zombonis in 4-10, either, so no, he doesn't need ice.
How strong are they? I'd suck to unlock them on Survival Endless if they're too powerful! On the other hand... if they're weaker than Gargantuars and their presence makes Gargantuar less likely to come out, it might be a boon instead!
Don't get your hopes up, his toughness is listed as "high", so he's as tough as the bucket head zombies (I'd have rated him the same as a cone head zombie, but I guess he's barely tougher than that).