Darmanitan zen mode - Page 2

It's not the least bit useful. It demands that you dedicate your move set to both ends of the spectrum lest you want to be dead in the water while in either, then it cuts your speed when you finally do transform, and that's the one stat you need above all else if you're going to be fighting with low health. The added defenses don't help at all because your HP is already at half or lower.

I reckon zen mode is great if used properly (my opinion)

As moveset goes:
Flame Charge (when your full hp it would be good to use a physical move that will also increase your speed when your in zen mode....1 or 2 flame charge should do the trick depending on the speed of your darmanitan)
Flamethrower/Fireblast (When your in ZenMode this will be your powerhouse moves)
Substitute (Good move once your in ZenMode since you have a ton of defense)
Psychic (A powerful Psychic move when your in Zen Mode since Darmanitan becomes Fire/Psychic

Item: Leftovers!! (Its good to balance your hp out with a bit of regeneration...taking advantage of Substitute, ZenModes Def and SpDef and Darmanitans high hp)