The clearest starting point is looking at these cards that have already been banned elsewhere
Pillar Analysis: High Power (Dual Land), Scarcity (Beta, Reserved List), Collector Scarcity
Teysa Karlov ($45-$70) This is focused on creature tokens, well see if the deck does a lot of other such things
Creature (9) 2x Adamaro, First to Desire 4x Birds of Paradise 3x Horizon Chimera Land (24) 2x Crumbling Necropolis 4x Evolving Wilds 6x Forest 2x Island 4x Mountain 4x Savage Lands 2x Swamp Enchantment (6) 2x Forced Fruition 4x Spiteful Visions Artifact (4) 4x Howling Mine Instant (13) 3x Cerebral Vortex 4x Fog 2x Gaze of Adamaro 4x Harrow Sorcery (4) 4x Toil / Trouble Pardon the unoriginal name and hilarious "curve", if you can call it that
I spend about 20% of my deck-construction time making very competitive decks, 60% designing balanced decks for our Commander league play, and 20% making super-casual decks that do silly or narrow things
It also plays very nicely with Harmonize due to its high power