Level 100 Statistics (see level 5, 50, 100)
Knock Off is evil, Rapid Spin is always useful, and Hidden Power Bug OHKOes Starmie and Celebi. Armaldo can be both a deadly sweeper and an excellent supporter thanks to Knock Off and Rapid Spin, as it has one of the best physically offensive typings in Bug / Rock. However, its weakness to Surf can prove a handicap.
This set functions as an offensive spinner. Hidden Power Bug is a solid STAB move, Rock Blast screws over Substitute users, while Rock Slide has greater accuracy. Swords Dance allows Armaldo to put the hurt on Dusclops and Gengar that try to come in and block Rapid Spin; even 252/252+ Dusclops is 2HKOed by +2 Rock Slide, so if its Will-O-Wisp misses or Rock Slide flinches, Dusclops is dead. Furthermore, if Dusclops runs more Special Defense investment, Armaldo can even Swords Dance on the switch, use Rock Slide as it is hit by Will-O-Wisp, and then KO Dusclops even with its reduced Attack, especially if given Spikes support. Earthquake is an alternative over Hidden Power Bug as it can hit Metagross and Tyranitar, and has good coverage alongside Armaldo's Rock STAB of choice. Rest allows Armaldo to survive for longer and function as a more reliable spinner.
Armaldo is a very slow Pokemon, so Speed investment is largely useless. You could give it a few Speed EVs so it outruns Swampert, but this is not really necessary. On the contrary, you should give it as much Attack and HP investment as possible, and put the rest in one of its defenses. In terms of HP EVs, 188 EVs—which yield a stat of 338—should be the minimum, as that allows Armaldo to survive four Seismic Tosses after Leftovers.
This is a similar set to the above, with Knock Off in place of Rapid Spin. Knock Off removes your opponent's item, which can prove extraordinarily useful: Skarmory, Blissey, and Suicune will all cry if Armaldo gets rid of their Leftovers. The combination of Knock Off and Rapid Spin would make Armaldo an amazing utility Pokemon, but they're unfortunately illegal together. This Armaldo works especially well with Salamence and Tyranitar; Knock Off the opposing Milotic's Leftovers and see how much it likes taking hard hits.
As with other Choice Band users, this Armaldo aims to hit foes hard. Knock Off's primary purpose is for when you aren't sure what your opponent will send out, as it will harm all Pokemon bar those with Sticky Hold. It also screws up foes such as Swampert, which Armaldo otherwise can't really hurt. Otherwise, attack as you see fit.
Checks and Counters
Water-types such as Suicune, Swampert, and Milotic counter Armaldo with ease thanks to their high Defense stats and access to STAB Surf. Slowbro can work too, but it has to be wary of Hidden Power Bug. Metagross easily KOes Armaldo with Meteor Mash and risks little outside of Earthquake. Steelix too can wall Armaldo all day if it doesn't have Earthquake, but a Swords Dance-boosted Earthquake can really screw it up. Claydol, Flygon, and Breloom stop Armaldo that run Earthquake and Rock Slide. All these Pokemon should beware of Knock Off, though.