Mythical Island breeding involves Mythical Monsters and the Cataliszt. Ethereal Monsters, including those with Rare Monster modifiers, can breed together, but this may lead to breeding failures. For example, Ghazt (Plasma) and Grumpyre (Shadow) don't guarantee a Whisp (Plasma + Shadow). Monsters like Natural, Seasonal, Mythical, Shugafam, and some Ethereal and Fire Monsters can be bred or bought. Breeding times differ based on the Monster combination.