Consider what your decks gameplan is, and what kind of cards it needs to perform that plan, then add in these situationally good cards based on the situations your strategy can run into
4 Esper Sentinel Whether its played early or late game, Esper Sentinel is excellent at drawing you cards
Legacy of the Duelist content!
This card is a huge difference maker in 2 weapon decks if used right, it is probably Guardian's most meta-defining card to the point it makes it really hard for the designers to make any sort of 'mid-grade' or 'backup' weapon in Guardian and heavily warps the card pool, but if you use it wrong it is going to make you miserable compared to running 4 weapons
That means that you can still run all of your favorite creatures with activated abilities while punishing your opponents for doing the same
Despite Yusho's attempt to keep him and Yuri apart, and his friends all having faith in him, Yuya ended up succumbing to Zarc's control right after he defeated Yuri