Since it cares about counters broadly, it even has sneaky synergy with persist and undying loops and with saga creatures
OUT: Manic Vandal, Oxidda Scrapmelter, Tuktuk Scrapper, Captivating Crew, Insurrection, Skyscanner, Clone Shell, Hoarding Dragon, Pilgrim's Eye, Ravenous Baboons, Flameshadow Conjuring, Magewright's Stone, Mimic Vat, Barrage of Expendables, Blasting Station, Culling Dais, Helm of Possession, Anger, Rowan, Fearless Sparkmage, and Goblin Engineer IN: Arcane Signet, Burnished Hart, Fire Diamond, Patriar's Seal, Wayfarer's Bauble, Chaos Warp, Firemaw Kavu, Spawn of Thraxes, Spitebellows, Tyrant of Kher Ridges, Altar of Dementia, Demonmail Hauberk, Jaxis, the Troublemaker, Rionya, Fire Dancer, Dollhouse of Horrors, Combustible Gearhulk, Firbolg Flutist, By Force, Shattering Spree, and Vandalblast
Glasswing Grace // Age-Graced Chapel
I concede this point
The best way for you to really grow Mowu to epic proportions is through the proliferate mechanic