The aforementioned Balduvian Warlords blocking clause is one example
Since Agent gives +1/+1 counters each time you attack the right person, you can really benefit from The Bastion of Karn, which can tap for four mana to proliferate and increase your counter count on your Commander
Heres a breakdown of the top categories of cards worth grading, from iconic staples to personal treasures
Creating a Rat at the beginning of your combat is a bit weaker in a four-player format, but Lord Skitter doesnt appear to be a high-priority removal target most of the time, so it can probably get away with creating some value
3 Mewtwo VSTAR (Crown Zenith: Galarian Gallery) A Pokmon favorite, Mewtwo is shown in its Mewtwo VSTAR card from the Crown Zenith: Galarian Gallery in the middle of a battle against Charizard and others
I always kept hold of my cards, but this one was especially important to keep hold of, and keep safe