Karsta, Plagued Hellkite

Flying, painborn
The first creature spell you cast each turn has painborn. (Each 1 life you pay while casting this pays for {1}. It enters the battlefield with a -1/-1 counter on it for each 1 life paid this way.)
At the beginning of each end step, remove any number of -1/-1 counters from another target creature onto another target creature.