When Three Tree Mascot enters, Haru triggers, targeting Three Tree Mascot as it is a land due to Toph.
Activate Shilgengar by sacrificing Three Tree Mascot.
When Three Tree Mascot dies, Haru triggers, returning Three Tree Mascot from your graveyard to the battlefield tapped.
When Three Tree Mascot enters, Haru triggers, targeting Three Tree Mascot as it is a land due to Toph.
Resolve the Shilgengar ability.
Repeat from step 3.
This clever loop turns your artifact ecosystem into an unstoppable engine by leveraging Toph, the First Metalbender, whose static ability turns all your nontoken artifacts into lands. Because Three Tree Mascot possesses changeling, it counts as an Ally, allowing its entry to trigger Haru, Hidden Talent and earthbend it into a creature-land. You then feed Three Tree Mascot to Shilgengar, Sire of Famine to generate a Blood token, which safely triggers its return to the battlefield via its own earthbend delayed effect. Repeating this cycle loops Three Tree Mascot endlessly between the battlefield and graveyard, capitalizing on Shilgengar's sacrifice outlet to produce infinite sacrifice and death triggers alongside a massive hoard of Blood tokens.