yugioh gilford the legend deck Yu-Gi-Oh Structure - Warrior's Triumph - Gilford the Rising by Every-Rush-Duel-Card

Scion of the Ur-Dragon Scion of the Ur-Dragon is a 5-colored card that can become a copy of one of your other powerful dragons

Good luck and have fun!

My personal favorite is still the Mystical Archive because it felt good in Limited formats (mainly being answers, not threats, but still interesting) and some spicy old cards like Channel included

TCGplayer TCGplayer is a fantastic place to grab singles

You can also probably get away with just running one copy in the deck if you have a card you use to add a little utility or support to your strategy, or one that you use as your silver bullet against certain strategies that are more common in the metagame

Cards will come from a variety of sets but mainly from the Commander sets