Level 100 Statistics (see level 5, 50, 100)
While Armaldo does possess above average stats, a wide variety of offensive options, and the ever-handy Rapid Spin, it is still a mediocre Pokemon. The biggest problem is that Armaldo requires a lot of support to be used effectively, as it fails to make use of its bulk due to its mediocre typing and cannot spin against the two top Ghost-type Pokemon in the tier—Golurk and Misdreavus—one-on-one. On top of that, Armaldo is too slow to reliably Rapid Spin without being revenge killed by faster Pokemon such as Samurott and Sawk. Armaldo does have one redeeming trait however: its ability, Swift Swim. With it, Armaldo is capable of beating most Ghost-types in the tier as well as outspeeding every Pokemon up to Zebstrika, all while still dealing good damage to most Pokemon in this offensive-inclined metagame. Despite its mediocrity, Armaldo can be put to good use on dedicated rain teams. On weatherless teams, however, Mold Breaker Sawk and Taunt leads such as Samurott and Misdreavus are much better at preventing hazards from going up on your side of the field.
This set should only be used on rain teams, where it can take on Regice and Kangaskhan, Pokemon that most rain teams have trouble with. Furthermore, Armaldo can now beat all Ghost-type Pokemon while also having a shot at pulling off a sweep once it nabs a boost. If you aren't using a rain team, you're better off with other Rapid Spin users such as Wartortle and Torkoal. Swords Dance boosts Armaldo's Attack stat to monstrous levels, turning it from an average Pokemon to a deadly sweeper in one turn if given the opportunity. Rock Blast provides a decent STAB move that can dent a bunch of Pokemon for good damage, and also gives Armaldo the ability to break through Substitutes and Focus Sashes; Lum Berry is the preferred item in this case as the utility that it provides comes in handy should Armaldo get crippled by status conditions such as Misdreavus's Will-O-Wisp. Stone Edge can also be used if you want a more consistent STAB move; however, it should only be used with Life Orb which allows Armaldo to hit hard and OHKO Misdreavus at +2. Aqua Tail in the rain acts like a psuedo-STAB move; it also has near-perfect coverage alongside Armaldo's Rock-type STAB and maims Golurk in the rain. Rapid Spin can remove hazards, such as Toxic Spikes and Stealth Rock, that are troublesome to rain sweepers.
Team Options & Additional Comments >>>
Any other choices for Armaldo are either terrible or severely outclassed. That said, if you insist on seeing this for yourself, there are a few select alternatives that you can make use of. If you're not using Armaldo in the rain for some odd reason, Battle Armor is the ability of choice. A physically defensive set with Stealth Rock / Rock Blast / Rapid Spin / Toxic or Knock Off might seem good on paper, but in reality, it fails to wall a good amount of prominent threats in NU, as Armaldo's typing is mediocre at best. X-Scissor is not recommended as Armaldo has trouble finding space for it, and the extra coverage is not that useful most of the time. It's quite sad that Armaldo learns Sunny Day but not Rain Dance, as it doesn't benefit from the sun at all. One thing that is useful to an extent is Rock Polish, which enables Armaldo's Speed to be boosted without rain. Armaldo also has access to other boosting moves such as Hone Claws and Curse, but most of the time, you're better off just attacking as these boosting moves aren't worth your while.
Checks and Counters
Offensive Water-type Pokemon, such as Samurott and Carracosta, can kill Armaldo with their STAB attacks. Metang and Seismitoad can take any hit from Armaldo and deal serious damage with their STAB moves. Tangela and Alomomola laugh at all of Armaldo's attempts at getting past them, as they can put it to sleep or hit it with a super effective attack, respectively; however, as Armaldo should be used on rain teams, it will have teammates that will likely get past that problem. Carracosta and Weezing can handle Armaldo well, but they should be wary after Armaldo gains a boost or two. While Armaldo can support a team by removing entry hazards, it has problems with them as Armaldo is weak to all of those entry hazards. Strong special attacks also hurt Armaldo greatly, but it does have enough bulk to take most neutral hits when at full health. Even with Rain up Armaldo is still very slow and is outspeed by common Choice Scarf users such as Jynx, Primape, Rotom-A, and Charizard, who can down Armaldo at low health.