It's true that there are essentially three "categories": no Game Changers, some Game Changers, and all Game Changers
Theres cards like Forsaken Monument for colorless decks and Maddening Cacophony for mill decks
Kraum, Ludevic's Opuss ability puts pressure on your opponents in two different ways: play more spells each round since the more they hold onto them to play later the more cards you get, OR : hold off on playing more than one spell a turn to keep from giving you any card advantage
Costing only four ink to play, Merlin, Goat triggers its Here I Come
Kirri, Talented Sprout Kirri, Talented Sprout does a great job supporting Yuma, Proud Protector in the desert precon and beyond, but I dont think much of it as a commander