Ishkanah dies, triggering Nim Deathmantle, causing you to pay ({4} magic symbol) to return Ishkanah from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Ishkanah enters the battlefield, creating three 1/2 Spider creature tokens.
Activate Ashnod's Altar by sacrificing a Spider, adding ({C} magic symbol) ({C} magic symbol) .
Repeat.
If you have black mana available, you may activate Ishkanah's ability to cause any number of opponent to lose life equal to the number of Spiders you control.