Is Jegantha, the Wellspring legal in Standard, Modern, and Commander?

Jegantha, the Wellspring is legal in: Legacy, Vintage, Commander, Historic. It is banned in: Modern, Pioneer.

Jegantha, the Wellspring

Q: What type of card is Jegantha, the Wellspring?

Jegantha, the Wellspring is a Legendary Creature — Elemental Elk. Its oracle text reads: "Companion — No card in your starting deck has more than one of the same mana symbol in its mana cost. (If this card is your chosen companion, you may put it into your hand from outside the game for {3} as a sorcery.) {T}: Add {W}{U}{B}{R}{G}. This mana can't be spent to pay generic mana costs."

Legendary Creature — Elemental Elk

Companion — No card in your starting deck has more than one of the same mana symbol in its mana cost. (If this card is your chosen companion, you may put it into your hand from outside the game for as a sorcery.)