The Temple Warrior is a card belonging to the Mercenaries, so you can use it in any of your squads regardless of the element of the hero selected to create it.
It is a card that can become a nightmare for the enemy thanks to its ability "Anger 1", with which it gets 1 attack point every time he receives an attack. Introducing the Temple Warrior into an Earth element squad with healing abilities can make for a very difficult combo to beat.