減衰球
アーティファクト
２点以上のマナを引き出す目的で土地が１つタップされるなら、それは他のタイプや点数の代わりに
を生み出す。
プレイヤーが各呪文を唱えるためのコストはそれぞれ、そのプレイヤーがこのターンに唱えた他の呪文１つにつき
多くなる。
スランの秘宝だが、１万年間まったく何もしていない。
イラスト：
Dominaria#213アンコモン日本語適正
裁定
If multiple replacement effects would modify what mana an ability you control produces, choose one to apply. After that, determine if any others are applicable. A replacement effect can’t apply to the same event more than once this way.
Damping Sphere’s second ability counts spells that were cast during a turn even if Damping Sphere wasn’t on the battlefield as they were cast. For example, if Damping Sphere itself is the third spell you cast in a turn, the next spell you cast costs 
more to cast.
To determine a spell’s total cost, start with the mana cost (or an alternative cost), add any cost increases, then apply any cost reductions. The spell’s converted mana cost remains unchanged, no matter what the total cost to cast it was.