Does a Chosen Champion need to be designated when registering a decklist, or can you choose between multiple legal Chosen Champions in your deck for game one?

Ruling: The Chosen Champion must be designated as part of deck registration and cannot be changed for game one. You cannot register multiple legal Chosen Champions and choose between them after revealing Legends.

Sequence:

• Chosen Champion is specified during deck registration as part of your main deck
• Game one must use the registered Chosen Champion
• Between games 2 and 3, you may change your Chosen Champion as part of sideboarding to a different champion from your deck or sideboard

Nuances:

• Deck registration requires "main deck including chosen champion", meaning the CC is a fixed part of the registered decklist, not just any legal champion present in the deck