Fine, you asked for it.
If you use this set, you're garbage. No exceptions. But if you absolutely positively must use Darmanitan-Z for some stupid reason this extremely gimmicky, extremely terrible, and extremely outclassed mixed attacker set can be kinda somewhat fun in some certain circumstances that you will likely never encounter, namely a circumstance where you have Trick Room set up and a free turn to use Belly Drum, and no strong priority attackers on your opponent's team. Why you would ever use this when things like Reuniclus and Rhyperior exist is beyond me, but hey, you asked for a Darm-Z set.
Darmanitan @ Life Orb / Petaya Berry
Quiet - Zen Mode
252 Attack, 252 Sp. Atk, 4 HP
IVs: 0 Speed
SEE? IT WORKS. Just ignore the fact that it did next to nothing and my opponents were all terrible.