First, I would suggest that Darmanitan will use Flare Blitz, as it gets boosted By Sheer Force, and I think that Charcoal is useless, either go with Choice Band, or Life Orb that gets boosted by Sheer Force.
Darmanitan@ Charcoal (Fire Punch)
[email protected] Band (Flare Blitz)
[email protected] Tag
The Attack EV's you gave me would not help if the Pokemon you're battling against is unknown, so it's a useless information.