Is Penregon Besieged legal in Standard, Modern, and Commander?

Penregon Besieged is legal in: Historic.

Penregon Besieged

Q: What type of card is Penregon Besieged?

Penregon Besieged is an Enchantment. Its oracle text reads: "At the beginning of your end step, choose a creature with the least toughness among creatures your opponents control. It perpetually gets -1/-1. When your opponents control no creatures, sacrifice Penregon Besieged."