When Dryad Arbor dies, Nim Deathmantle triggers, causing you to pay ({4} magic symbol) to return Dryad Arbor from your graveyard to the battlefield, and attaching Nim Deathmantle to it.
When Dryad Arbor enters the battlefield, Nesting Dragon triggers, creating a 02/ Dragon Egg creature token.
Activate Ashnod's Altar by sacrificing the Dragon Egg, adding ({C} magic symbol) ({C} magic symbol) .
When the Dragon Egg dies, it triggers, creating a 2/2 Dragon creature token.