With this bug, we can obtain a damage output that surpasses the Ice Ball Shuckle scenario in Gen 6, even without triple battles where two Helping Hands and Flower Gifts were in play. The cool thing about this is that instead of a Shuckle, the only Pokemon capable of achieving this combination is
A GEN 3 PIKACHU WITH EGG MOVE 'CHARGE', transferred over to SM.
So, why Pikachu, and in particular, Gen 3? Well, in order for this particular combination to work, Pikachu needs to have 3 important moves that are Move Tutor moves only obtainable in Emerald: Defense Curl, Rollout, and Mimic. "Yeah, but many Pokemon can learn those moves, including Shuckle that can reach 614 Attack". Well, the difference comes with held items. In order for the "6th hit" with the 32x multiplier to work, Metronome (the item) will not be able to add the item multiplier unless Shuckle uses Rollout again (which sucks because the 32x multiplier goes to a 30BP move). Light Ball, on the other hand, adds the x2 multiplier no matter when and what move is used.
"But Pikachu's max attack is 229! It's too small!" Well, thanks to Power Split, Shuckle can raise a Pokemon's attack stat to 613 attack by using it in tandem with Power Trick. After using this combination 10 times, ANY Pokemon will eventually have 613 Attack.
Basically, Pikachu will have an attack stat that is really similar to Power Trick'd Shuckle, but unlike Shuckle it will be able to use any move to have the 32x multiplier while keeping the 2x item multiplier thanks to Light Ball. What is the move going to be? It will be Power Trip, that will be called using Me First, that will be learned using Mimic. Also, Heliolisk will use Electrify on Pikachu so that Power Trip will become an Electric-type move, and Pikachu will use Charge the turn before so the damage is doubled even further, and Electric Terrain will be in play.
The target will be a Level 1 Smeargle that used Reflect Type to get Water/Flying typing, and has Power Trip. Smeargle is handy because it can have any move and at Level 1 and -6 debuffs it'll have 1 Defense stat anyway.
Start the Double Battle. First, Pikachu will be Power Splited until it reaches 613 Attack, Skill Swapped Huge Power, uses Rollout (1 of the moves will hit disguise) to activate the Rollout-Disguise bug, learns Me First via Mimic, and gets +6 on all stats so that Power Trip has 860BP. Pikachu also uses Charge the turn before the BIG HIT.
Right next to Pikachu will be Flower Gift Cherrim who uses Helping Hand while the sunlight is harsh.
On the other side, Heliolisk will use Electric Terrain the turn before, and uses Electrify on Pikachu so that Pikachu's attacks will all become Electric Type that turn.
Right next to the Heliolisk is the target Level 1 Smeargle at -6 Defense with Water/Flying typing, who uses Power Trip on Pikachu so that Pikachu's Me First will turn into Power Trip.
A Charge + Me First + Helping Hand + Flower Gift-Boosted Electric Type 860BP Power Trip that is boosted by a factor of 32 under Electric Terrain from a 613 Attack Huge Power Pikachu holding a Light Ball hits a Level 1 Water/Flying Smeargle with -6 Defenses...and the move crits. This is going to hurt.
After careful damage calculations taking order of operation seriously (since sadly the online damage calc doesn't let you input 27520 BP), I got the following number. (Note: the Shuckle column is for the Triple Battle Ice Ball against a Forest's Cursed Noibat, for comparison. Green multipliers affect the BP, Red multipliers affect the attack stat, and white multipliers are applied after base damage is calculated.)
This move does 20,660,732,484 DAMAGE. I don't know how the game handles damage numbers, but since Int is limited to a little over 2 billion, I'm not sure if the game is able to handle damage of this degree LOL. This assumes Me First doesn't mess up the Rollout-Disguise bugged multiplier, but even then you can just Mimic Power Trip instead and still end up with 13,773,821,656 damage, which is still way above the Shuckle scenario in Generation 6, even if you tried to abuse the Symbiosis glitch.