Is Runeforge Champion legal in Standard, Modern, and Commander?

Runeforge Champion is legal in: Modern, Pioneer, Legacy, Vintage, Commander, Historic.

Runeforge Champion

Q: What type of card is Runeforge Champion?

Runeforge Champion is a Creature — Dwarf Warrior. Its oracle text reads: "When this creature enters, you may search your library and/or graveyard for a Rune card, reveal it, and put it into your hand. If you search your library this way, shuffle. You may pay {1} rather than pay the mana cost for Rune spells you cast. Power/Toughness: 2/3"

Creature — Dwarf Warrior

When this creature enters, you may search your library and/or graveyard for a Rune card, reveal it, and put it into your hand. If you search your library this way, shuffle.

You may pay rather than pay the mana cost for Rune spells you cast.