I think that all possible mates are Nightwhisper, Fallenfeather, Cottonwillow, Dustfeather, Duskfall, if you want to have kits. If you don't mind not having kits with them, then you can also be mates with Nightmare and Breezesong. I haven't played the game through very thoroughly in a while, so idk about Cookie or Max, but in previous editions you could mate and have kits with them too. In previous editions, you could be mates & have kits with Goldenwillow, as well as have kits with Nightmare, but cannot anymore. Hope this helps!