Your Main Deck can include up to 3 copies of the same named card. 1. This includes your Chosen Champion. Example: A deck could include Volibear, Furious as its Chosen Champion and still include 2 more copies of Volibear, Furious in their Main Deck. 2. Cards have different names even if they represent the same character. Example: A deck could include 3 copies of Yasuo, Remorseful and 3 copies of Yasuo, Windrider, because they have different names.
§ 103.2.b Core Rules PDF (officieel)
§ 103 To play Riftbound, a player must have a Main Deck, a Rune Deck, a Champion Legend, and a number of Battlefields determined by the Mode of Play. These are collectively referred to as a player’s deck.
§ 103.2 A Main Deck of at least 40 cards: A Chosen Champion Unit, as well as Units, Gear, and Spells
