Activate Ashnod's Altar by sacrificing Birthing Hulk, adding CC.
When Birthing Hulk dies, Nim Deathmantle triggers, causing you to pay 4 to return Birthing Hulk from your graveyard to the battlefield and attach Nim Deathmantle to it.
When Birthing Hulk enters, it triggers, creating two creature tokens.
Activate Ashnod's Altar by sacrificing a creature token, adding CC.
Repeat.
This clever loop turns the mechanical harmony of Birthing Hulk, Ashnod's Altar, and Nim Deathmantle into an engine of endless value. When you sacrifice Birthing Hulk to Ashnod's Altar, the two Eldrazi Scion tokens it originally brought along—along with the mana from the altar—provide the exact resources needed to fuel Nim Deathmantle's resurrection trigger. By sacrificing those very same Eldrazi Scions to Ashnod's Altar for more mana, you can easily pay the four-mana resurrection cost to bring Birthing Hulk right back to the battlefield, where it immediately spawns a fresh batch of tokens to repeat the cycle infinitely.