Gahros, the Manarender

When Garhos enters the battlefield, he gets a
-1/-1 counter.
{1}, {t}: Add X {c} to your mana pool, where X is
the number of -1/-1 counters on Gahros.
Then put a -1/-1 counter on Gahros.
Whenever one or more mana is added to a player's
mana pool from a source that isn't Gahros, that
player loses 1 life.