Ariados

Insomnia
Prevents sleep.
Swarm
Boosts power of Bug-type moves 50% when at 1/3 HP or less.
Type Tier
Bug / Poison NU
Statistics
Min- Min Max Max+
HP
70
- 281 344 -
Atk
90
194 216 279 306
Def
70
158 176 239 262
SpA
60
140 156 219 240
SpD
60
140 156 219 240
Spe
40
104 116 179 196
Name Item Ability Nature

Baton Pass

Focus Sash / Salac Berry Insomnia Adamant
Moveset EVs
~ Spider Web / Agility
~ Baton Pass
~ Sucker Punch
~ Bug Bite / Toxic Spikes / Endure
4 HP / 252 Atk / 252 Spe

Ariados is the only Pokémon (bar Smeargle) to learn both Spider Web and Baton Pass. However, you may prefer to use Agility due to Ariados' incredibly low Speed, which would make it easier to pull off a Baton Pass. Sucker Punch hits Ghosts and Psychics hard, and Bug Bite may pick up extra boosts from Liechi or Salac Berries, which would come as a welcome boost. However, Toxic Spikes provides more team support, and can help wear things down. It also works well if you trap a Pokémon that does nothing against Ariados, as you can set up with ease. Using Endure with Salac Berry may help pull off a successful Baton Pass. Poison Jab can be used in this slot, but is generally seen as a weaker option. You can use an alternate, more defensive EV spread of 220 HP / 252 Def / 36 SpD, which lets you survive a Jolly Choice Band Primeape's Stone Edge. It also takes advantage of Ariados' 4x Fighting and Grass resistances. Ariados can alternatively run an Impish nature with this defensive EV spread.

Name Item Nature

Choice Band

Choice Band Adamant
Moveset EVs
~ Poison Jab
~ Bug Bite
~ Sucker Punch
~ Pursuit / Toxic Spikes
4 HP / 252 Atk / 252 Spe

This set takes advantage of Ariados's only decent stat: Attack. Poison Jab provides decent STAB, and is likely to OHKO many frail sweepers, such as Swellow and Ninetales (although the latter needs Stealth Rock support). Bug Bite backs it up, while possibly picking up extra boosts. You may get a Swarm boost too, though Insomnia may be more the more reliable ability. Sucker Punch makes up for Ariados' awful Speed, and can OHKO many weaker Pokémon. The last slot can go for either Pursuit or Toxic Spikes (if you ever find the time to do the latter). Pursuit will do a minimum of 86% to a fleeing Grumpig and a minimum of 78% to Hypno.

Other Options

There aren't many. Agility can work with Life Orb. Shadow Sneak can be used if you are worried about things setting up on Sucker Punch.

EVs

Ariados should run 252 EVs in Attack and Speed, or use the EV spread 220 HP / 252 Def / 36 SpD. The latter provides more bulk, but the former is more offensive. Impish with the defensive EV spread provides even more bulk on top of this. 172 EVs in Speed can work with Agility, allowing you to outspeed all base 95 Pokémon after a boost.

Opinion

Ariados' stats are, in general, awful. However, should you pull of a Spider Web pass, Ariados will not have been useless. His Attack can cause some hurt, provided you aren't taken out first. Insomnia is nice to help take sleep, though, and often helps pull off a Baton Pass.

Counters

Most things in general. Steel- and Fire-types are best. Aggron and other physical walls shrug off the Choice Bander with ease; they just have to be careful of Spider Web. Camerupt and Ninetales can come in moderately easily, and cause pain with their STAB Fire attacks. Damage from Stealth Rock can add up quickly, so try to take advantage of this.