Tenacious Dead | Pitiless Plunderer | Umbral Collar Zealot (and one other card)

Cards

Activate
Umbral Collar Zealot by sacrificing
Tenacious Dead.
When
Tenacious Dead dies, it,
Skittering Precursor, and
Pitiless Plunderer trigger.
Resolve the
Pitiless Plunderer trigger, creating a Treasure token.
Resolve the
Skittering Precursor trigger, creating a creature token.
In response to the remaining trigger, activate
Umbral Collar Zealot by sacrificing the creature token.
When the creature token dies,
Pitiless Plunderer triggers, creating a Treasure token.
Resolve the
Umbral Collar Zealot 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
Umbral Collar Zealot ability from step 1.
Repeat.

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