Did you know? The most effective combo in Pokemon is the most inefficient, but it involves this very two-move combo itself.
Firstly, you need the right Pokemon --
Meditite/Medicham/Azurill/Marill/Azumarill + any other Pokemon with Skill Swap
Cherrim with Helping Hand + Sunny Day
Shuckle with Power Trick + Defense Curl + Rollout and held Metronome item, maxed DEF EVs.
Any Pokemon with Screech / Tail Whip, etc.
Any Pokemon with Swords Dance + Baton Pass
This only works in a double battle. You want to first Baton Pass +6 ATK to Shuckle. Then, you want to Skill Swap Medicham's ability onto Shuckle and have Shuckle use Power Trick. Afterward, send in Cherrim, set up Sunny Day and have Shuckle use Defense Curl. Retreat and use Screech for -6 DEF on an enemy while Shuckle attacks the foes with Rollout. Send Cherrim back out and use Helping Hand on the 5th Rollout. If the foe is a level 1 Yanma or Ledyba and it has negative nature, no IVs or EVs, and you land a critical hit, you should do 213,896,052 damage to it.
Your Shuckle will have:
Base 230 ATK
+50% to ATK from Pure Power
+300% ATK from Swords Dance
+50% ATK from Flower Gift
960 base power Rollout 5th hit from Defense Curl
+50% more power on Rollout from Helping Hand
+50% more power on Rollout for STAB
+300% damage from 4x weaknesses of foe
+100% damage from critical hit
+50% more damage from Metronome item
-300% defense on foe from Screech