The Mountain is often sideboarded out if they dont have Path to Exile effects or you dont need red mana
Its easy for a niche card to be strong within its niche - and sometimes a card like that is simply so strong that it takes a deck from being a fun idea into a crushing way to play Commander - but its far rarer for a card to work in decks that its not intended for
Like most other "Toon" Monsters, "Toon Cannon Soldier" can attack the opponent directly while they don't control a "Toon" Monster
Drannith Magistrate, Sanctum Prelate, Archon of Emeria, Lavinia, Azorious Renegade, Boromir, Warden of the Tower, Aven Mindcensor & Containment Priest shut down a LOT of strategies
Area Zero Underdepths [Stellar Crown] could also be an interesting tech card, as long as you are able to find space for a Tera Pokmon in the deck