Convoke, delve (Each creature you tap while casting this spell pays for or one mana of that creature's color. Each card you exile from your graveyard pays for .)
You may cast this card from your graveyard.
Trample
Hogaak fills the graveyard, then casts itself for free over and over using convoke and delve, acting as a recursive 8/8 trampler and a fodder engine for sacrifice and reanimator strategies. Early turns dump creatures into the bin via self-mill and discard, midgame loops Hogaak as a body or sac fodder, and late game grinds opponents out with attrition and incidental drain.
Commander that costs zero mana and recurs from the graveyard, dodging color-screw and providing a relentless body
Synergizes perfectly with self-mill, which fuels its own delve while filling reanimation targets
Resilient to spot removal and counterspells since it just comes back from the yard
Trample plus easy convoke/delve makes it both a beater and free sacrifice fodder for aristocrats