What would you do to fix darmanitan’s zen mode ability in a way that’s thematically appropriate?
Hmm. Well, the problems with Zen Mode as I see it are:
1) you’re forced to train one Pokémon to fill two roles, and wind up splitting EVs, nature and move sets so you get this messy hybrid (I think Game Freak did anticipate this and tried to deal with it by giving the two forms extremely high base stats in the areas they specialise in – the problem is you’re better off just piling EVs and a nature bonus on top of the high stats enjoyed by the basic form and pushing his attack into the goddamn stratosphere), and 2) Zen Darmanitan is a tank who inherently starts with less than 50% health, which compromises his usefulness. Well, and 3) the alternative, Sheer Force, is such a hugely powerful ability for a Pokémon with a stat spread as extremely specialised towards physical damage as Darmanitan’s, but there’s not much we can do about that.
I think 2) is best solved by switching the forms around, having Darmanitan absorb damage with his tanky Zen form and then shift into his regular mode to strike back. There could be flavour-related reasons for not doing this, but I’m not sure what those might be. 1) is trickier. I sort of want to treat Darmanitan’s forms as two separate Pokémon – probably make them have the same nature and IVs (compare the way Shedinja works) but allow them to learn moves and do EV training separately. Dunno how powerful that winds up being in the end – I think probably pretty strong, but since it’d function differently to anything else we have right now it’s hard to gauge it. Bear in mind, of course, that it has to be really strong to compete with the sheer damage output of Sheer Force. Not sure where the balance point is, though…