Karnors - Unmezzable Skeleton Mobs
 

Tried to mez skeletal guardians and skeletal scryers 30+ times yesterday, not a single one landed. 50 bard, using Crisson's pixie strike. I don't recall these mobs being unmezzable, although a quick google search did not result in information either way.

Were they level 46+? Pixie strike won't work against 46+ mobs (although it should work, according to evidence I recently posted).

These npcs do not have an immune to mez flag set for them, so I concur with Lazortag the issue is probably the spell being cast.