monarch 1st edition booster box Grand Archive TCG Flesh and Blood - Monarch

A card can be valuable because it is powerful in one of these formats, especially Commander, which has a huge casual player base and constant demand for unique cards

Additionally, Twilight Masquerade and Temporal Forces have shown to have great cards for competitive play as well

Note that this is a little different than the Near-Mint/Slightly-Played/Heavily-Played paradigm used by retailers selling Magic cards

Do counters stay on creatures in the graveyard

Do you have a Red legendary creature as your Commander who has an ETB ability

the buff ability plus this commanders keywords suggest a Voltron strategy, but the latter ability rewards you for going wide