Evil Patron

Evil Patron is earned by completing the Boneyard with a Cleric cat. This unlocks the Evil Patron passive ability, which flips the Cleric's role by making healing abilities deal damage to enemies instead, while also granting +2 range on tile-targeted healing spells. The upgraded version doubles all Holy element damage you deal, creating enormous offensive potential from a class normally built around support. Combines powerfully with Blessing of Holy Fire for up to a 4x Holy damage multiplier (as long as your cat has not yet killed a unit that battle). Upgrading Evil Patron is generally more valuable than upgrading Blessing of Holy Fire for this synergy.