Activate Yahenni by sacrificing Reassembling Skeleton.
When Reassembling Skeleton dies, Pitiless Plunderer and The Skullspore Nexus trigger, creating a creature token and a Treasure token.
Resolve the Yahenni ability.
Activate Yahenni by sacrificing the creature token.
When the creature token dies, Pitiless Plunderer triggers, creating a Treasure token.
Resolve the Yahenni ability.
Activate the Treasures by tapping and sacrificing them, adding 1.
Activate Reassembling Skeleton by paying 1, returning it from your graveyard to the battlefield.
Repeat.
This clever recycling loop turns the humble Reassembling Skeleton into an infinite engine for sacrifice and death triggers, fueled entirely by the mana generated when things perish. As you repeatedly send the Skeleton to the graveyard, Pitiless Plunderer converts each of those demises into a fresh Treasure token to pay the resurrection costs. Meanwhile, Yahenni, Undying Partisan grows ever more massive with every creature that falls—while also being able to step in as a sacrificial outlet should you need to feed the engine extra tokens. Finally, The Skullspore Nexus watches the nontoken deaths unfold, spinning out increasingly massive Fungus Dinosaur tokens that not only scale its own casting discount but also keep the sacrifice fodder flowing endlessly.