Bloodflow Connoisseur

Sacrifice a creature: Put a +1/+1 counter on Bloodflow Connoisseur.

Demonic Rising

At the beginning of your end step, if you control exactly one creature, create a 5/5 black Demon creature token with flying.

Homicidal Seclusion

As long as you control exactly one creature, that creature gets +3/+1 and has lifelink.

Fettergeist

Flying
At the beginning of your upkeep, sacrifice Fettergeist unless you pay {1} for each other creature you control.

Lone Revenant

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
Whenever Lone Revenant deals combat damage to a player, if you control no other creatures, look at the top four cards of your library. Put one of them into your hand and the rest on the bottom of your library in any order.

Peel from Reality

Return target creature you control and target creature you don't control to their owners' hands.

Predator's Gambit

Enchant creature
Enchanted creature gets +2/+1.
Enchanted creature has intimidate as long as its controller controls no other creatures. (It can't be blocked except by artifact creatures and/or creatures that share a color with it.)

Mist Raven

Flying
When Mist Raven enters, return target creature to its owner's hand.

Bone Splinters

As an additional cost to cast this spell, sacrifice a creature.
Destroy target creature.

Alchemist's Apprentice

Sacrifice Alchemist's Apprentice: Draw a card.

Demonic Taskmaster

Flying
At the beginning of your upkeep, sacrifice a creature other than Demonic Taskmaster.