Do cards with the same name replace each other when played (such as playing a second Traveling Merchant or champion cards like Jinx 'Rebel')?

Ruling: No cards ever get replaced when played. You can have as many copies of a card in play as you like, regardless of whether they share the same name or are champions.

Nuances:

• While you can have multiple copies in play, you can only include three copies of any card in your original deck construction.