Activate Ashnod's Altar by sacrificing Callous Bloodmage, adding CC.
Callous Bloodmage dies, triggering Nim Deathmantle, causing you to pay 4 to return Callous Bloodmage from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Callous Bloodmage enters the battlefield, creating a 1/1 Pest creature token.
Activate Ashnod's Altar by sacrificing the Pest, adding CC.
When the Pest dies, it triggers, causing you to gain one life.