High Rock Summoner can be purchased with the Ancano's Cunning deck or purchased alone for 100 soul gems.
High Rock Summoner herself is not that powerful. However, its power is extremely useful when you are in need of strong cards, every Atronach the card summons is a heavy hitter. A good strategy is to use this card in conjuction with Actions (Legends) that summon this creature again, like A Night to Remember (Legends), activating its summon ability again.
She may place one of the following into the player's hand: