Is Imprison legal in Standard, Modern, and Commander?

Imprison is legal in: no major formats. It is banned in: Legacy, Vintage, Commander.

What type of card is Imprison?

Imprison is an Enchantment — Aura. Its oracle text reads: "Enchant creatureWhenever a player activates an ability of enchanted creature with {T} in its activation cost that isn't a mana ability, you may pay {1}. If you do, counter that ability. If you don't, destroy Imprison.Whenever enchanted creature attacks or blocks, you may pay {1}. If you do, tap the creature, remove it from combat, and creatures it was blocking that had become blocked by only that creature this combat become unblocked. If you don't, destroy Imprison."

Imprison

Enchantment — Aura

Enchant creature<br>Whenever a player activates an ability of enchanted creature with in its activation cost that isn't a mana ability, you may pay . If you do, counter that ability. If you don't, destroy Imprison.<br>Whenever enchanted creature attacks or blocks, you may pay . If you do, tap the creature, remove it from combat, and creatures it was blocking that had become blocked by only that creature this combat become unblocked. If you don't, destroy Imprison.