Activate Ashnod's Altar by sacrificing Mausoleum Guard, adding CC.
When Mausoleum Guard dies, it and Nim Deathmantle trigger,
Resolve the Mausoleum Guard trigger, creating two creature tokens.
Holding priority, activate Ashnod's Altar by sacrificing a creature token, adding CC.
Resolve the Nim Deathmantle trigger, causing you to pay 4 to return Mausoleum Guard from your graveyard to the battlefield and attach Nim Deathmantle to it.