Heartstone

Activated abilities of creatures cost {1} less to activate. This effect can't reduce the mana in that cost to less than one mana.

Grim Guardian

Constellation — Whenever this creature or another enchantment you control enters, each opponent loses 1 life.

Blessing of Leeches

Flash
Enchant creature
At the beginning of your upkeep, you lose 1 life.
{0}: Regenerate enchanted creature.

Hateful Eidolon

Lifelink
Whenever an enchanted creature dies, draw a card for each Aura you controlled that was attached to it.

Lust for War

Enchant creature
Whenever enchanted creature becomes tapped, this Aura deals 3 damage to that creature's controller.
Enchanted creature attacks each combat if able.

Agent of the Shadow Thieves

Commander creatures you own have "Whenever this creature attacks a player, if no opponent has more life than that player, put a +1/+1 counter on this creature. It gains deathtouch and indestructible until end of turn."

The Brute

Enchant creature
Enchanted creature gets +1/+0.
{R}{R}{R}: Regenerate enchanted creature.

Xantcha, Sleeper Agent

Xantcha enters under the control of an opponent of your choice.
Xantcha attacks each combat if able and can't attack its owner or planeswalkers its owner controls.
{3}: Xantcha's controller loses 2 life and you draw a card. Any player may activate this ability.