In an Un- game, if X is actually infinite (Urza's Fun House is a pathway to many game states some consider to be unnatural), you can assume that every natural result on a six-sided die is rolled infinite times, leading to infinite Clown Robot tokens and infinite +1/+1 counters on Clown Car
Sideboard has a decent amount of interaction though
Kroxa and Kunoros Kroxa and Kunoros is another card that sees play in a ton of formats, and is one of a cycle of two existing legendary creatures that have were combined in March of the Machine : specifically Kroxa, Titan of Death's Hunger and Kunoros, Hound of Athreos, both cards from Theros Beyond Death
Runner-Up : Energy Energy was first created as a mechanic in original Mirrodin , but there wasn't enough space for it, so it was pulled
The stars of the show are the new Alolan Exeggutor and Flygon Stellar Tera-type cards, alongside Latias ex, Gouging Fire, and Dialga