Volcanic Hammerer and Hazy Flame Hyppogrif are the "best" targets for it I guess. They both kinda suck, though. Hammerer and Thestalos have the highest ATK of anything you can Summon with it. Not really worth using, Pyro-Types kinda suck.
So if I double tribute for flame emperor then use the crater to get two headed dragon out of my hand via special sum. It should work right? But in duel links it's refusing even though it literally a tutorial for this.