Sisterhood of Karn is a rare Creature — Cleric card from Doctor Who (WHO), collector number 399. Current market price: $0.38 (foil $0.36), TCGplayer market prices via Scryfall.
This creature enters with a +1/+1 counter on it. Paradox — Whenever you cast a spell from anywhere other than your hand, double the number of +1/+1 counters on this creature.