When playing Mythos of Nethroi after the new update, the game won't allow you to pay it's GW cost to destroy any nonland permanent. Instead, it only gives you the option to pay 2B when targeting a non-creature permanent, and gives you the option to pay with GW only when targetting creatures. I play on PC, and I have Log attached of my last game where I tried to use it on a planeswalker and it wouldn't give me the option.