Tenacious Dead | Pitiless Plunderer | Goblin Bombardment (and one other card)

Cards

Activate
Goblin Bombardment by sacrificing
Tenacious Dead.
When
Tenacious Dead dies, it,
Sifter of Skulls, and
Pitiless Plunderer trigger.
Resolve the
Pitiless Plunderer trigger, creating a Treasure token.
Resolve the
Sifter of Skulls trigger, creating a creature token.
In response to the remaining trigger, activate
Goblin Bombardment by sacrificing the creature token.
When the creature token dies,
Pitiless Plunderer triggers, creating a Treasure token.
Resolve the
Goblin Bombardment ability from step 5.
Activate two Treasure tokens by tapping and sacrificing them, adding ({B} magic symbol) ({B} magic symbol) .
Resolve the
Tenacious Dead trigger, paying ({1} magic symbol) ({B} magic symbol) to return it to the battlefield from your graveyard.
Resolve the
Goblin Bombardment ability from step 1.
Repeat.

This combo has been estimated to be Exhibition (Bracket 1+).