His direct and pure damage based utility makes him appealing in most places and his low mana costs further increase his desirability
The second clause I think is the better one because as long as this is tapped, no one can swing at you with an army
Then for each creature card you own in exile with a memory counter on it, create a tapped and attacking token that's a copy of it
Most multiplayer players are running mass removal in their colors, so if you exile Damnation, Wrath of God, Austere Command and Blasphemous Act you get one for sure
Grand Coliseum Five-color decks and commanders that care about you taking damage will love Grand Coliseum, and its easy to see why
Anybody who runs their hands over the rich, polished surface of Magic long enough becomes intimately familiar with the burrs, those weird cards which generate trivia questions and allow for unforeseen interactions to arise