The sun school has a mutate spell, simply use the fire wyvern mutate spell card on an ice wyvern spell card in your hand. It will then convert the ice wyvern spell card to a temporary fire wyvern treasure card.
In order to acquire this mutate spell you have to find the mutate master, he is hidden in celesta somewhere. I suggest having a fire wizard and making ice his secondary school, that way you can use power pips to cast your new spell. Or have a fire mastery amulet... that works too.
using this method you can cast as many fire wyverns as your deck will allow, the trick is having the original spell and the mutate spell in your hand at the same time.
The sun school has a mutate spell, simply use the fire wyvern mutate spell card on an ice wyvern spell card in your hand. It will then convert the ice wyvern spell card to a temporary fire wyvern treasure card.
In order to acquire this mutate spell you have to find the mutate master, he is hidden in celesta somewhere. I suggest having a fire wizard and making ice his secondary school, that way you can use power pips to cast your new spell. Or have a fire mastery amulet... that works too.
using this method you can cast as many fire wyverns as your deck will allow, the trick is having the original spell and the mutate spell in your hand at the same time.