A player can only Equip one Mystic (anointed NFT) at a time.
A player with an equipped Mystic gains that mystic type (maybe its Moon, or Moon+Shadow if its a dual mystic) and the current Power level of the mystic.
When an Anointed NFT is equipped to a player, that player can participate in OnChain games.
There are also non Anointed NFTs that can be played with (they have one mystic type and power level of 0) - but, they cannot be played in any On-Chain games. Only Anointed NFTs can play on-chain.
So if UserA is creating a deck of cards with friends. If those friends have non-anointed NFTs equipped then UserA will have to swap those players out before they want to earn any On-Chain rewards.