Activate Ashnod's Altar by sacrificing Dryad Arbor, adding CC.
When Dryad Arbor dies, Nim Deathmantle triggers, causing you to pay 4 to return Dryad Arbor from your graveyard to the battlefield, and attaching Nim Deathmantle to it.
When Dryad Arbor enters the battlefield, The Necrobloom triggers, creating a 0/1 Plant or a 2/2 Zombie creature token.
Activate Ashnod's Altar by sacrificing the creature token, adding CC.