OMG! The players in my game utterly trashed the grikkitogs!
Once they realized what the monsters could do, retreating back to the basement once after a brief skirmish, they used their reflection of water resonant reflection to flood the grikkitog's cavern AND outer hallway.
This forced the monsters to either hide in stone (there is no indication they can breath while earthgliding) or come out of their implantation and face the heroes more directly.
In the end one was reduced to 10 hit points and drowned. The other was grappled and held in the water, thrashing wildly until it too drowned.