Necronomicon Altar

At the beginning of your end step, if an opponent lost one or more creatures, Amass Skeletons {1}.

{t}, Exile Necronomicon Altar and artifacts you control called Necronomicon Ex Mortis, Naturom Demonto I, and Naturom Demonto II: Create The Watcher, an 8/8 Legendary Zombie Demon creature token with Indestructible and all triggered abilities of the exiled cards.