Damping Sphere
Artifact
If a land is tapped for two or more mana, it produces 
instead of any other type and amount.
Each spell a player casts costs 
more to cast for each other spell that player has cast this turn.
A Thran relic, it has spent ten thousand years doing absolutely nothing.
イラスト：
Dominaria#213アンコモン英語適正
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.