Is Storm Seeker legal in Standard, Modern, and Commander?

Storm Seeker is legal in: Legacy, Vintage, Commander.

What type of card is Storm Seeker?

Storm Seeker is an Instant. Its oracle text reads: "Storm Seeker deals damage to target player equal to the number of cards in that player's hand."

Instant

Storm Seeker deals damage to target player equal to the number of cards in that player's hand.

Set Legends

Rarity Uncommon

Artist Mark Poole

Instant Commander Legacy Vintage