Blade Knight was in Tin Series 1 in 2004, while Exarion Universe was in Tin Series 2 alongside Rocket Warrior and Panther Warrior etc. Which those two are sadly not included in the card pool, either. Most People in the goat community agree that even if you argue that maybe Exarion is legal, when there is no card legality precedent, it is a format shifting card due to its high stats on both ATK and DEF and the ability to pierce through things like goat tokens. There are already cards people run to remove tokens, and Exarion would mostly outclass them all.
As far as a best deck goes,