Caelum
qibz official stalker
Kinda got this idea after use SubPetaya Yanmega, and on my paralysis UU team this thing has done extremely well. Gotta thank skiddle also for giving some thoughts on the set as well.
Edit: There is a modified version posted below, please refer any corrections to that one, not this.
http://www.smogon.com/dp/pokemon/mothim
[SET]
name: SubSwarm
move 1: Substitute
move 2: Bug Buzz
move 3: Air Slash
move 4: Shadow Ball / Energy Ball
item: Petaya Berry
nature: Timid
evs: 4 Def / 252 SpA / 252 Spe
[SET COMMENTS]
<p>This set is one time use only; if brought out too soon in a battle it will fail to sweep, so use it intelligently. Bring this out late game when your opponents team has been softened up and proceed to Substitute down to activate Swarm and the Petaya Berry. Surprisingly, Stealth Rock actually doesn't cripple this set, since after one Substitute, Swarm and the Petaya Berry will activate. From there, Mothim can proceed to sweep with a +1 SpA Bug Buzz boosted by Swarm. Air Slash complements this for additional STAB. Shadow Ball is essentially for Rotom, but Energy Ball is also a decent option to better handle Steel types; such as Probopass and Steelix, who are neutral to Grass but resist Bug. It is recommended that you surround this with paralysis support since Mothim isn't very fast and this can limit its sweeping potential.</p>
<p>If surrounding this with paralysis support doesn't appeal to you, switching to a Salac Berry over a Petaya Berry is viable. However, the drop in power will be noticeable in many cases.</p>
Edit: There is a modified version posted below, please refer any corrections to that one, not this.
http://www.smogon.com/dp/pokemon/mothim
[SET]
name: SubSwarm
move 1: Substitute
move 2: Bug Buzz
move 3: Air Slash
move 4: Shadow Ball / Energy Ball
item: Petaya Berry
nature: Timid
evs: 4 Def / 252 SpA / 252 Spe
[SET COMMENTS]
<p>This set is one time use only; if brought out too soon in a battle it will fail to sweep, so use it intelligently. Bring this out late game when your opponents team has been softened up and proceed to Substitute down to activate Swarm and the Petaya Berry. Surprisingly, Stealth Rock actually doesn't cripple this set, since after one Substitute, Swarm and the Petaya Berry will activate. From there, Mothim can proceed to sweep with a +1 SpA Bug Buzz boosted by Swarm. Air Slash complements this for additional STAB. Shadow Ball is essentially for Rotom, but Energy Ball is also a decent option to better handle Steel types; such as Probopass and Steelix, who are neutral to Grass but resist Bug. It is recommended that you surround this with paralysis support since Mothim isn't very fast and this can limit its sweeping potential.</p>
<p>If surrounding this with paralysis support doesn't appeal to you, switching to a Salac Berry over a Petaya Berry is viable. However, the drop in power will be noticeable in many cases.</p>