Unique

Unique is a talent which prevents several units with the same name to be in play at the same time.

If a player casts a Unique unit when there already is one with the same name on their side of the board, then the existing one is destroyed. This does not affect other types of units, including those with the Unique trait but whose name is different. This does not affect opponent's units either.

In-game description
Spawning a Unique destroys previous Uniques with the same name.