Chittering Witch dies, triggering Nim Deathmantle, causing you to pay ({4} magic symbol) to return Chittering Witch from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Chittering Witch enters the battlefield, creating at least three 1/1 Rat creature tokens.
Activate Phyrexian Altar three times by sacrificing three Rats, adding ({3} magic symbol) .