DISCLAIMER: I haven't played Singles since Gen 4, so bear with me.
Ariados is pretty atrocious, but I think this is a cool time to bring up an idea I've had in the past: is there a way for a Pokemon to abuse the ability Swarm (or Overgrow, Torrent, etc.)? I've always thought that Swarm was pretty cool in theory, as I've pictured it as a whole bunch of other bugs showing up to help out their pal when the going gets tough. Ariados needs some reinforcements.
Let's start by giving our poor little spider bro a brand-new signature move:
Spider Bite - Acc: 100 - BP: 65 - the power of this move increases in a pinch
When Ariados is below 25% health, the power of this move spikes to base 100. Pretty useless when Ariados has a decent amount of health left, but lethal when paired with Swarm and perhaps a Salac or Liechi Berry. This gives Ariados its best chance of sweeping (or at least doing something) when below 25% health. There are basically 2 ways to pull this off:
SPIDER SWARM
Ariados @ Salac Berry/Liechi Berry
Ability: Swarm
EVs: 252 Atk / 4 Def / 252 Spe
Adamant/Jolly Nature
- Substitute
- Spider Bite
- Poison Jab
- Fell Stinger/Night Slash/Shadow Sneak
This is a Sub set, allowing Ariados to Sub itself down to Swarm/Spider Bite/Berry, finally allowing it to be in a position to do some sort of damage. Spider Bite, effectively 225 BP at this point including STAB and Swarm, is the main source of damage, with Poison Jab as an alternate STAB. The last slot is a choice, with Fell Stinger getting cool points and the chance to rack up a boost or 2 to do even more damage.
SPEEDY SPIDER SWARM
Ariados @ Focus Sash
Ability: Swarm
EVs: 252 Atk / 4 Def / 252 Spe
Adamant Nature
- Agility
- Spider Bite
- Poison Jab
- Fell Stinger/Night Slash/Shadow Sneak
With this set, bring Ariados in on something that can comfortably OHKO it. Proceed to Agility on the ensuing attack, putting yourself at +2 Speed with Swarm Spider Bite ready to go, and then commence firing off Spider Bites. This set is a little tougher to pull off as it is checked by hazards and priority, but has more sweeping potential because of the easy boosts.
So that's my idea for a pretty terrible Pokemon. It will probably still be relegated to the lower tiers of Singles play, but at least now it's a little more fun to use!