Spiteful Squad has at least one +1/+1 counter on it.
Steps
1Activate Ashnod's Altar by sacrificing Spiteful Squad, adding .
2Spiteful Squad dies, triggering itself, Felisa and Nim Deathmantle.
3Resolve the Spiteful Squad trigger, moving its +1/+1 counters onto another creature you control.
4Resolve the Felisa trigger, creating a 2/1 Inkling creature token for each counter that was on Spiteful Squad.
5Activate Ashnod's Altar by sacrificing an Inkling, adding .
6Resolve the Nim Deathmantle trigger from step 2, causing you to pay to return Spiteful Squad from your graveyard to the battlefield, and attach Nim Deathmantle to it.