Garnok’s spell will end the game if he is the last troop and it causes him to die. This is despite the fact that he summons a troop. It’s similar to the Elspeth bug that was supposed to have been fixed. In the background of the below you can see that I won the game from Garnok killing himself despite him having summoned Fel’dras
Edit: and yes I was testing @mraider94 's team against my own defence 