Blood Seeker

Whenever a creature an opponent controls enters, you may have that player lose 1 life.

Rampaging Ferocidon

Menace
Players can't gain life.
Whenever another creature enters, Rampaging Ferocidon deals 1 damage to that creature's controller.

Vigilance
A player losing unspent mana causes that player to lose that much life.
{1}, {T}: Each player adds {B}{R}{G}.

At the beginning of each end step, each player discards their hand.