Maybe some kind of partner assist mechanic? Called for help in Alola. Why not expand on that? Swings battles too much by entering the battle directly, probably, even for a limited time. Could shoot for a less direct implementation.
Designates a 7th Pokemon as a supporter. Cannot switch into this Pokemon normally during a battle. Displays this Pokemon at the start of battle. Visibly stands/sits with you during battles, as a nice cosmetic bonus. Provides your opponent some information to strategize around, also.
Some ideas on assist options:
- Trigger the assist Pokemon's ability (Intimidate, Drought, Neutralizing Gas, Cloud Nine...)
- Use one of the Pokemon's non-damaging moves (Trick Room, Heal Pulse, Soak, Aromatherapy, Skill Swap, Imprison, Tailwind...)
- Type Attack cheer. Boosts moves of that Pokemon's type by 30% for X turns for all allied Pokemon.
- Type Defense cheer. Reduces damage from moves of that Pokemon's type by 30% for X turns for all allied Pokemon.
- Sideboard. Removes your current Pokemon from the battle. Tags in the assist Pokemon. Does not activate abilities like Intimidate. Cannot bring the switched-out Pokemon back into the match.
Likely needs to limit the assist to once per battle. May need workshopping beyond that too. Imagines Spore being a popular supporter move otherwise. (Maybe Pure Power Skill Swap too?) Also seems thematically strange to allow a Pokemon on the sidelines to heal or put opponents to sleep without being in danger.
For competitive purposes: Brings a team of 6 battle Pokemon and 3 supporters. Cannot designate a Pokemon as a battle Pokemon AND a supporter Pokemon.