Leechling

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.)
Mulch (When this creature dies, you may return another creature card with toughness equal to or greater than the number of -1/-1 counters on this card from your graveyard to your hand.)
Whenever a card you control is put into a graveyard, put a -1/-1 counter on Leechling.