Core Prowler dies, triggering itself and Nim Deathmantle.
Resolve the Core Prowler trigger, causing you to proliferate.
Venser triggers, creating a legendary 3/3 The Hollow Sentinel artifact creature token.
Activate Ashnod's Altar by sacrificing The Hollow Sentinel, adding ({C} magic symbol) ({C} magic symbol) .
Resolve the Nim Deathmantle trigger from step 2, causing you to pay ({4} magic symbol) to return Core Prowler from your graveyard to the battlefield, and attach Nim Deathmantle to it.