Sensor Splicer dies, triggering Nim Deathmantle, causing you to pay ({4} magic symbol) to return Sensor Splicer from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Sensor Splicer enters the battlefield, creating a 3/3 Phyrexian Golem creature token.
Activate Ashnod's Altar by sacrificing the Phyrexian Golem, adding ({C} magic symbol) ({C} magic symbol) .