Question: If the Battle Bond was an actual mechanic/gimmick in game, how would you make it work?

Battle Bond became a dark horse of sorts, something that only appeared very few times yet people fell in love with it.

There was a rumor saying that Battle Bond would be a thing in Legends ZA but it's non-official, it said that Battle Bond would give Pokemon a Rainbow Aura that boosted their stats, and it would have different levels.

This got me thinking, what if this was an actual thing in a Pokemon game? How would you guys make this mechanic work?

For me? I would keep the Rainbow Aura and Stats Boost thing, but when we achieve it's highest level, the Pokemon gains a new form. Said new forms would be a simple pallete change and a headgear, similar to what Ash-Greninja.

The colors and Headgear would be based on what your character is wearing, and perhaps, if possible, take it a step further and make the Battle Bond form something customizable, allowing the players to decorate and decide how the powered-up form of their favorite Pokemon would look like.

Please feel free to share your ideas and opinions with me.