When submitting a deck for competition, must you declare your champion unit, and does this differ between Bo1 and Bo3 formats?

Ruling: In Bo1 you must always play the same champion unit that was declared during deck submission. In Bo3, after sideboarding, the champion unit can be changed.

Nuances:

• The champion unit must be made known during deck submission
• Bo3 format allows champion flexibility after sideboarding, while Bo1 does not