I know it's not really on theme, but I want to recommend a Dust Elemental, because infinite combo with Ghalta, Stampede Tyrant (and any one other creature with an ETB effect).
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Urza's Saga final ability can tutor out Didgeridoo. Possible replacement for the Mishra's Factory?
This deck seems too focused on just the amass mechanic. It could probably be split into at least two different decks. Just brainstorming here, but Invade the City, Lazotep Plating, Honor the God-Pharaoh, Commence the Endgame, maybe Toll of the Invasion, seem like they would be more at home in a near-creatureless deck seeking to Polymorph or Transmogrify the token into some huge threat, with the backup plan of using the token itself, buffed to enormous size by Invade the City.