Withercrown

Enchant creature
Enchanted creature has base power 0 and has "At the beginning of your upkeep, you lose 1 life unless you sacrifice this creature."

Painful Quandary

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

Underworld Dreams

Whenever an opponent draws a card, Underworld Dreams deals 1 damage to that player.

Swamp

The Scorpion God

Whenever a creature with a -1/-1 counter on it dies, draw a card.
{1}{B}{R}: Put a -1/-1 counter on another target creature.
When The Scorpion God dies, return it to its owner's hand at the beginning of the next end step.

Sickle Ripper

Wither (This deals damage to creatures in the form of -1/-1 counters.)

Kaervek the Merciless

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