After performing the Leader Action, if the enemy has the required Active Runes, it performs the Rune Action. It can perform any of the 4 main actions: Sail a Boat, Explore with a Settler, Harvest, or Build.
It cannot perform any other type of action. Instead, the enemy performs that Rune’s Action listed on its Enemy Clan Mat. For example, the enemy cannot perform the "Discard and Replace a Card" action, so it instead performs its mat’s action. Active Runes required for the action can come from its Island Runes and Viking Cards in both its Leader Row and Battle Row (see If You Start the Battle).