How to deal with Gremlion ?

[Zechnophobe]

So, against K'tahu your first turn as a mage should be to cast stone skin on two of your stacks. Same with your second turn. Don't attack with melee users unless against his weak spot, until you have stone skins up. Keep only one or two stacks hitting him, while the rest deals with his friends.

Trolls with Stone Skin are just about unkillable by ktahu.