Spiteful Squad dies, triggering itself, Felisa and Nim Deathmantle.
Resolve the Spiteful Squad trigger, moving its +1/+1 counters onto another creature you control.
Resolve the Felisa trigger, creating a 2/1 Inkling creature token for each counter that was on Spiteful Squad.
Activate Ashnod's Altar by sacrificing an Inkling, adding ({C} magic symbol) ({C} magic symbol) .
Resolve the Nim Deathmantle trigger from step 2, causing you to pay ({4} magic symbol) to return Spiteful Squad from your graveyard to the battlefield, and attach Nim Deathmantle to it.