Bell Borca, Spectral Sergeant
Legendary Creature — Spirit Soldier
Note the mana value of each card as it's put into exile.
Bell Borca's power is equal to the greatest number noted for it this turn.
At the beginning of your upkeep, exile the top card of your library. You may play that card this turn.
イラスト：
Dominaria United Commander#145レア英語適正
裁定
Bell Borca notes converted mana costs only if it’s on the battlefield as a card is put into exile.
Look at the card in exile, not its previous zone, to determine its converted mana cost.
If a card in exile has 
in its mana cost, X is considered to be 0.
While not on the battlefield, and before any cards are noted for it each turn, Bell Borca’s power is 0.
You must follow the normal timing permissions and restrictions for the card exiled by Bell Borca’s last ability. If it’s a land, you can’t play it unless you have land plays available.
You’ll still pay all costs for a spell cast this way, including additional costs. You may also pay alternative costs if any are available.
If you don’t play the exiled card, it remains exiled.