Herald Of The Swarm

Devoid, Ingest
On your upkeep, create a 1/1 colorless eldrazi scion with "Sacrifice this creature: Add {c}."
{c}, {t}: add {c} to your mana pool for each eldrazi scion and spawn you control.
When Herald Of The Swarm dies, return it to the battlefield as an enchantment with on your upkeep, create a 1/1 colorless eldrazi scion with "Sacrifice this creature: Add {c}." for each eldrazi scion and spawn you control.