Is Thassa's Rebuff legal in Standard, Modern, and Commander?

Thassa's Rebuff is legal in: Modern, Pioneer, Legacy, Vintage, Commander.

What type of card is Thassa's Rebuff?

Thassa's Rebuff is an Instant. Its oracle text reads: "Counter target spell unless its controller pays {X}, where X is your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)"

Thassa's Rebuff

Instant

Counter target spell unless its controller pays , where X is your devotion to blue. (Each in the mana costs of permanents you control counts toward your devotion to blue.)