Grandpa can react to, move and block a beam of light in Capsule Monsters
https://vsbattles.fandom.com/wiki/User_blog:RapidMotorcycle19/Yu-Gi-Oh!_Capsule_Monsters
source, its a very unprofessional blog but does detail the series ep by ep
b-but muh 4kids.
Tom and Jerry Chase.
Overall, i think Ash will win if they give him the infinite reaction speed from Cynthia and not give Yugi his vs Jaden Infinite speed duel in a timeless dimension.
Otherwise, Yugi can also react to Elemental Hero Neos blocking a blast from satorius all the way from his moon in neptune to earth in seconds, which is MFTL+
youtube.com/watch?t=432&v=n2QyFyqeIKQ&feature=youtu.be
https://imgur.com/a/i9oz6l3
https://imgur.com/a/wCjZKyu