Brine Comber dies, triggering Nim Deathmantle, causing you to pay ({4} magic symbol) to return Brine Comber from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Brine Comber enters the battlefield, creating a 1/1 Spirit creature token.
Activate Ashnod's Altar by sacrificing the Spirit, adding ({C} magic symbol) ({C} magic symbol) .