I'm surprised this guy seems to be seen as kind of weak. Admittedly, I've yet to really delve into competitive battling for this gen beyond the Random Battles, but it seems like Mudsdale should have a lot of potential with the stamina ability. I do think it might actually work best in doubles with some kind of skill link or beat up strategy, but its singles ability shouldn't be underestimated. Like others have mentioned, an AV set is probably the best option for now. It would be nice if it got some utility moves or a little more coverage, but I still think it can work well.
Mudsdale @ Assault Vest
Ability: Stamina
EVs: 252 HP / 252 Atk / 4 Defense
Adamant/Impish/Careful Nature
- Earthquake/Bulldoze
- Close Combat/Superpower/Low Sweep
- Heavy Slam
- Rock Slide/Payback/Body Slam
This isn't super different from other sets, but I did want to show some different options to consider. Bulldoze is a lot weaker, but it is still STAB off a 125 Attack and has the effect of slowing down your opponent so you've got that speed control game going. Both CC and SP are quite powerful, but the defense drops one each kind of go against what you're trying to accomplish with Mudsdale (mainly being a bulky tank) so Low Sweep is something to look at cause again you can lower the speed of an opponent and potentially force a switch. Heavy Slam is a great move since you are so heavy, and will more often than hit with a 120 BP move, which'll smash most fairies.
Rock Slide deals with Flying types, obviously, like the Charizards of the world and such, which is handy. It is essentially EdgeQuake coverage which is quote good. Payback works since you are gonna hit last most every turn, unless you are running trick room, then one of the two other moves would be best. Body Slam doesn't get you super effective hits obviously, but it will still hit hard with the chance to paralyze. Mainly I'm trying to think of ways to speed control with this mudsdale as well as just hit hard and tank hits.
The EVs and nature can be adjusted as needed. I personally think what is there is best, but if you wanted to remove some attack EVs and make it more specially or physically defensive as needed, it can definitely work. Same with the nature. Adamant is best just for dealing damage, but if you wanted to do some kind of mixed spread with a impish or careful nature depending, it is an option to be sure.
Sadly, there's not a ton else Mudsdale can do for now, though I do think the AV set works. I did want to try and piece together some kind of utility set for our horsey bud.
Mudsdale @ Smooth Rock/Leftovers/Chesto Berry
Ability: Stamina
EVs: 252 HP / 4 Atk / 252 Sp.Def
Relaxed Nature
- Sandstorm
- Roar/Toxic
- Earthquake
- Rest/Substitute/Rock Slide
Basically a discount hippowdon set, which I don't think is the greatest use of Mudsdale. If you want an alternate sand-setter, then Mudsdale can potentially work. Ideally, you'd want to set sand, then decide what to do depending on what moves you choose. I think Roar works for the phazing capabilities. If you already have stealth rock up, then phazing that and the chip damage from sandstorm can be annoyance. Toxic can work if you're trying to play a more stallier game, and spreading status is never bad. You want Earthquake for STAB, obviously, then the last move is up to you, and dictates what item you use. Rest is your only form of recovery, sadly, so a chesto-resto set can work in conjunction with Stamina. You can take a few physical hits, rest, and then wake up at full health with your defense boosts.
Substitute is an option just to add to your overall bulky nature. When using substitute, leftovers will be your preferred option for that sustainability. Rock Slide is an option just for the sake of coverage, and so flying types don't completely wall you out. Another item choice that won't lead you astray is smooth rock, just to extend sandstorm. That works best obviously when making a strict sand team so do be sure to keep that in mind.
The EVs are best suited for your mixed bulk, I would say. With the stamina ability, your defense will be rising naturally anyway, so it's best to go full sp. defense though a relaxed nature will give your defense that slight boost which can be really useful. As before, if you did want to adjust to be physically defensive from the get-go, you are free to. Ultimately, I do feel like the AV set is probably the best option, but this certainly isn't a terrible set either.