Breeding Pit

At the beginning of your upkeep, sacrifice Breeding Pit unless you pay {B}{B}.
At the beginning of your end step, create a 0/1 black Thrull creature token.

Ebon Praetor

First strike, trample
At the beginning of your upkeep, put a -2/-2 counter on Ebon Praetor.
Sacrifice a creature: Remove a -2/-2 counter from Ebon Praetor. If the sacrificed creature was a Thrull, put a +1/+0 counter on Ebon Praetor. Activate only during your upkeep and only once each turn.

Thrull Surgeon

{1}{B}, Sacrifice Thrull Surgeon: Look at target player's hand and choose a card from it. That player discards that card. Activate only as a sorcery.

Endrek Sahr, Master Breeder

Whenever you cast a creature spell, create X 1/1 black Thrull creature tokens, where X is that spell's mana value.
When you control seven or more Thrulls, sacrifice Endrek Sahr, Master Breeder.

Culling the Weak

As an additional cost to cast this spell, sacrifice a creature.
Add {B}{B}{B}{B}.

Dark Ritual

Mourning Thrull

({W/B} can be paid with either {W} or {B}.)
Flying
Whenever Mourning Thrull deals damage, you gain that much life.

Thrull Champion

Thrull creatures get +1/+1.
{T}: Gain control of target Thrull for as long as you control Thrull Champion.

Basal Thrull

Death Pit Offering

When Death Pit Offering enters, sacrifice all creatures you control.
Creatures you control get +2/+2.

Swamp

Armor Thrull

{T}, Sacrifice Armor Thrull: Put a +1/+2 counter on target creature.

Soul Exchange

As an additional cost to cast this spell, exile a creature you control.
Return target creature card from your graveyard to the battlefield. Put a +2/+2 counter on that creature if the exiled creature was a Thrull.

Thrull Retainer

Enchant creature
Enchanted creature gets +1/+1.
Sacrifice Thrull Retainer: Regenerate enchanted creature.