Do you have to start a game with a chosen champion unit on your board, or can the chosen champion zone be empty?

Ruling: In constructed formats, you must have a chosen champion that matches your legend. In sealed format, you are not required to have a legend or champion card, and if you're missing either or both, you draw an extra card on first turn.

Nuances:

• In sealed format, you can use 3 colors and your chosen champion does not have to match the legend (e.g., Ahri Legend with Nocturne in champion zone)
• There is likely no strategic reason to leave the chosen champion zone empty in constructed, as having an extra card in hand is valuable