Zantar the Drowned

Zantar the Drowned enters the Battlefield with
X +1/+1 counters on it.
Discard a card: Put a +1/+1 counter on Zantar.
Put a -1/-1 counter on Zantar: Draw a card.
Put a +1/+1 counter on Zantar: Draw a card.
Only an opponent may activate this ability.
Discard a card: Put a -1/-1 counter on Zantar.
Only an opponent may activate this ability.