Kykar's limitation to trigger only on noncreature spells is hardly restrictive, given so many other available spell types
Killing planeswalkers and gaining massive loyalty, stealing dorks that are too powerful or just smashing up lands each turn are all good ways of beating the various archetypes
If you still want a theme beyond legendary cards are strong, Jodah Superfriends seems like an interesting angle that would get in a bunch of proliferate cards alongside powerful planeswalkers like Teferi, Hero of Dominaria, Nicol Bolas, God-Pharaoh, and Oko, Thief of Crowns
Deny someone their Sunforgers search and cast while still unattaching the equipment, stop that Senseis Divining Top from going to the top of their library, or allow an opponent to sink 50 health into their Aetherflux Reservoir only for you to counter the ability and stop them from dealing 50 damage to you