IV-training and competitive battling aside, sometimes I feel training your Pokémon in battle is too straight-forward and controlled. I’d like to see a mechanic where even a wild-caught Pokémon occasionally disobeys its trainer’s command (maybe it “slacks off” or uses a different move altogether) or feels overwhelmed / flinches and returns to its Pokéball for an ally to replace it. And this becomes less likely the more trust (higher friendship value) a given Pokémon has towards its trainer until it fades away once High Friendship (value 200) is achieved. Keep in mind each Pokémon species is assigned a base friendship level when caught so disobedience could be more pronounced for certain species (which naturally feature a lower baseline friendship value when caught) than others. I’d especially like to see this play out in pseudo-legendary lines, legendary/mythical Pokémon, and maybe special versions of certain species – regardless of how many badges you have (obedience according to your number of collected badges could remain a separate mechanic specific to traded Pokémon).
So, I think this changes the “vibe,” if you will, considerably. I suspect if you just implement mechanics like this in the core Pokémon games as they currently exist, and don’t also add some kind of additional systems for developing your relationship with your Pokémon that come with associated benefits, players would unreservedly hate it. It’s a whole extra mechanic standing between us and what we already understand to be “normal” battling, which makes the game much harder – but in a random and frustrating way, not in a way you can be strategic about. I appreciate the goal here, making your friendships with your Pokémon something you really have to work at, but there’s got to be more to it, carrots and not just sticks, and ways of working around the disadvantages.
Having said all that, if you wanted to rebuild Pokémon to be a much more punishing and painful game all around – something in the spirit of the Nuzlocke challenge, for instance – this mechanic might be an interesting addition as it stands; something that will, from time to time, just randomly cause you to lose a Pokémon and force you to adapt to that loss. Throw in Nuzlocke staples like permanent death and limited, randomised Pokémon choice; reduce access to Pokémon Centres and sharply limit healing items (maybe lock high-quality healing behind some kind of crafting system); add some permanent debilitating conditions (so, like, less experienced Pokémon might disobey you, but more experienced Pokémon might also have picked up scars or developed phobias that give them specific weak points); remove some of the quality-of-life stuff from the last few generations like easy EV training methods… maybe then we’ve got a game on our hands. Either way, it’s got to be part of a package of mechanics with a definite theme and feel, is the point.