Is Frontier Siege legal in Standard, Modern, and Commander?

Frontier Siege is legal in: Modern, Pioneer, Legacy, Vintage, Commander.

What type of card is Frontier Siege?

Frontier Siege is an Enchantment. Its oracle text reads: "As this enchantment enters, choose Khans or Dragons. • Khans — At the beginning of each of your main phases, add {G}{G}. • Dragons — Whenever a creature you control with flying enters, you may have it fight target creature you don't control."