Dungeons 4

didnt unlock for me, while playing coop --> restarted solo and it workd fine.

Same problem Coop killing heros in two different mission didn't count

Yep the achievement doesn't pop in co-op :( but work fine in solo

190 kills, 121 spells cast, solo, achievement didn't pop. Bugger.

Also seems to be glitched for me solo.

EDIT: Ok so I managed to unlock this not sure if this was the solution but what I did was played on easy, followed the game through the tutorial, up to the point you unlock your first "Arcane Tear", I never activated this ability in the previous playthrough on both occasions, since I have played this level again and activated the"Arcane Tear" ability the achievement has now popped, I only used Meteor Shower spell (LT on controller) AFTER I activated Arcane Tears (press the view button to activate Arcane Tears first). popped pretty much straight after 20 kills in game, this was also all done out of the underworld and on solo.

What I think it means by spells in the description is have arcane tears activated and get 20 kills with other spells while that is activated at a guess?

Hopefully this helps someone else having similar issues.

the simple answer to this glitched achievement is that if you ever used a load in your game it will stop working.
I noticed that the counter said 4/20 after killing the second group of enemies. But I had forgotten to use spells on the very first enemies you encounter. And because I wasn't sure how many enemies there were in the level, I reloaded. From then on the counter didn't go up from 0/20. When I restarted the whole level it worked again.