Ophiodancer

Painborn (Each 1 life you pay while casting this spell pays for {1}. This creature enters the battlefield with a -1/-1 counter on it for each 1 life
paid this way.)
At the beginning of your end step, target opponent creates X 1/1 black and green Snake creature tokens with "At the beginning
of your upkeep, you lose 1 life." Where X is the number of -1/-1 counters on Ophiodancer.