Well since everyone is doing move sets, I'll take a shot at counters.
Heatran is as usual, one of the first ones to come to mind. It can switch into Flare Blitz and send an Earth Power back. Omastar, Sharpedo and Kabutops get nice switch in opportunities off of Flare Blitz, and send back strong Hydro Pumps, Earth Powers, Aqua Jets, Waterfalls and Stone Edges. Dragonite with Aqua Jet is a pretty safe switch in with Multiscale. Dugtrio is a nice and easy revenge killer. Starmie outruns and wrecks it with it's water STAB attacks. Thunder Wave shuts down most sweeping attempts, so fast carries of this move, such as Jolteon, Ambipom, Zebstrika, etc. can be useful. Bulky Water types are good choices, because 140 Base Attack and Sheer Force is scary to switch into, even though they'll take huge hits regardless. Blastoise, Cloyster, Swampert, Carracosta carry high Defense, but you can always expand to others such as Vaporeon, Lanturn, Lapras, Quagasire. Frankly, it's hard to counter something this fast and strong unless you can heavily reduce the damage you take on a switch in or score a revenge kill. There are plenty of things that outrun Darmanitan, but on the Choice Scarf variants, that window shuts to a near close.
This is a signature that doesn't eat up an absurd amount of space.