The thrulls bred at a terrifying pace. In the end, they overwhelmed the Order of the Ebon Hand.

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.

The List

Duel Decks Anthology: Divine vs. Demonic

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

Duel Decks: Divine vs. Demonic

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

Masters Edition

Fifth Edition

During your upkeep, pay o
Bo
B or bury Breeding Pit.
At the end of your turn, put a Thrull token into play. Treat this token as a 0/1 black creature.

Breeding Pit must actually be on the battlefield at the beginning of the endstep in order for you to get a Thrull. The getting of the Thrull is not part of paying the upkeep, it is part of having the card on the battlefield.