How to always deal 7,777 damage.

There are 4 stages you must complete.

1 - Obtain the enemy skill materia.

2- Obtain L4 Suicide Enemy Skill

3 - Obtain the Chocobuckle Enemy Skill.

4 - Escape from a lot of battles and max out your HP.

The earliest point in the game that you can obtain the enemy skill materia is in Shinra HQ. At Hojo's lab inside the sample tank where Aeris and RedXIII are held, after the boss battle look inside for the yellow thing lying on the floor.

Another early point in the game it can be obtained (but easily missable) is the beginners hall in Junon.

Once you have the Enemy Skill materia, it's time to get the L4 suicide and Chocobuckle Enemy Skill. Go to the Chocobo Ranch, on the world map near this area you will fin the enemy Mu. Keep defending and healing until you learn L4 suicide.

Go inside the ranch and speak to the trader in the barn, learn about catching Chocobos. Buy the Chocobo Lure materia along with a Mimett or Sylkis Green. Other greens wont work for what we want to do here.

Equip your lure materia and go south of the Ranch onto the chocobo footprints. We are looking for a lv 16 chocobo. This can be determined by using the scan ability, or an easier method is if a Chocobo spawns with 2 Elfadunks or 2 Levrikons, that means the Chocobo is lv 16.

With a lv 16 Chocobo, immediately use a Mimett Green or Sylkis Green on it, now cast the L4 suicide ability. This will force the Chocobo to use the Enemy Skill Chocobuckle.

The next stage is the longest and most boring part. To use the All Lucky 7's ability, your HP needs to be dead on 7,777. Chocobuckle will deal 1 damage for every battle you escape from.
You can either escape from enough battles for your chocobucle ability to deal 1,111 or 2,222 damage.

Once this is achieved, use the ability on a party member with maxed out HP, 9,999. This will reduce their HP to 7,777 therefore activating the All Lucky 7's ability.

Me personally do not have the time to escape from lots of battles, but this is how you do it :)