Activate Ashnod's Altar by sacrificing Diregraf Horde, adding CC.
Diregraf Horde dies, triggering Nim Deathmantle, causing you to pay 4 to return Diregraf Horde from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Diregraf Horde enters the battlefield, creating two 2/2 Zombie creature tokens.
Activate Ashnod's Altar by sacrificing a Zombie, adding CC.