All Lucky 7s is a special Easter Egg status that appears only in Final Fantasy VII. It occurs when a character's HP lands on exactly 7,777, causing an in-battle message to say "All Lucky 7s". When this happens, the character begins rapidly attacking all enemies in the battle, with each of the 63 hits doing exactly 7,777 damage. The character cannot be controlled during this barrage of attacks. The character's name also begins to flash in the battle menu. Afterward, all subsequent attacks will always hit for 7,777 damage until the character's HP changes. After the battle ends, the character's HP falls to exactly 1, so that the effect cannot happen infinitely.
If an enemy is defeated during the barrage of 63 attacks, the character in the status will stop attacking that enemy, however the death animation will not play until the barrage of attacks is finished. If multiple characters fall into the status at the same time, they will take it in turns to attack. Each character can only unleash the barrage attacks once per battle, and while they can leave and re-enter the status, only the effect of inflicting 7,777 damage will occur.
Note that enemies can also enter a Lucky 7 state, where all of their attacks will do 7,777 damage upon connecting with the player, making it an extremely dangerous state.
If a player is in both the All Lucky 7s status and the Poison status at the same time, they will take 7,777 damage from the Poison and die. This is because the damage taken from Poison is as if it were inflicted by the player to themselves.
As the chances of All Lucky 7s happening spontaneously are low, the player can manipulate the character's HP to get it to 7,777 to trigger the status. The best is of course, if one manages to manipulate a character's Max HP to 7,777, but this is difficult to achieve, as HP growth is randomized. If the player has less than 7,777 HP they can try to get the last two digits of a character's HP to 77 (for example by being hit by mini or frog enemies), and then use Potions and Hi-Potions to get the HP to 7,777. An easy way to get to 7,777 HP is in the battle against Emerald Weapon; Emerald Weapon's Aire Tam Storm deals 1,111 damage per equipped Materia; a character with 9,999 HP needs to take 2,222 damage to get to 7,777, which is easily achieved from Aire Tam Storm by equipping two Materia on said character.
If Cloud enters the final one-on-one battle with Sephiroth with 7,777 HP, the attacking spree phase will not activate.