These are some random ideas I got, share if you wish.
Characters are not interchangeable for free during the bout. Certain conditions have to be met. For example.
Characters will have a character swap combo ender. This ender does not cash out, but leaves the opponent either staggered or flipped out. That is one of the few moments were the characters can be switched.
Shadow character swap wakeup: Spend one bar with a wake up move that lets you change your character. This shadow move is treated as a wakeup DP, very unsafe on block.
To encourage character swapping, and to make the bouts shorter and more intense, the first team to lose a character, loses the fight. This is made to avoid using one character during the whole fight and then changing to the other only when the first dies. Creative character swapping is the goal of this mode.
Characters can call their partner for a shadow assist mode. This assist is treated as an ARIA assist. The assistant character receives damage if tagged, but can’t be comboed.
Shadow combo breakers and shadow counter breakers: The shadow breaker breaks the combo while also swapping character. This breaker does indeed damage to the opponent. The shadow counterbreaker swaps characters while giving a 5 second lockout, as normal.
If a shadow counterbreaker catches a shadow combo breaker, both opponents get caught in the combo during the lockout. Whih means both opponents can be ultra’d at the same time.