Hogaak, Arisen Necropolis earned its spot on the list for its brief notoriety following MH1s release, where it held Modern in a stranglehold
Kefner's Last Word: With enough artifact mana rocks, the tap penalty can be minimized
Witch-King of Angmar Another five-drop is my top spot
Effects like card draw and lifegain can be extremely powerful, and some Limited and Constructed decks use blink or flicker effects to repeatedly trigger creatures' ETB abilities
It gives us back-to-back enchantments of the Gruul persuasion
Matoya, Archon Elder is a sweet draw engine, and I can see her fitting into Kenessos sea creatures, Tales of Middle-earth blue-green decks like Elrond and Galadriel, and shell also just generally be a good engine piece in graveyard strategies that surveil a lot, like Mirko, Obsessive Theorist