Furnace of Rath

If a source would deal damage to a permanent or player, it deals double that damage to that permanent or player instead.

Kaervek the Merciless

Whenever an opponent casts a spell, Kaervek the Merciless deals damage equal to that spell's mana value to any target.

{T}: Heartless Hidetsugu deals damage to each player equal to half that player's life total, rounded down.

At the beginning of each end step, each opponent loses life equal to the life they lost this turn. (Damage causes loss of life.)

Whenever an opponent casts a spell, that player loses 5 life unless they discard a card.