All Lucky 7's is a special status in Final Fantasy VII. When a character's HP is reduced to 7777, he/she will receive the All Lucky 7's effect. The character will go into a super-attack mode, hitting the enemy around fifty times for 7777 points of damage each time. Obviously this means that your character's HP must be above 7777 to get this chance. After the battle, the character's HP is reduced to 1 (this is the game's way of avoiding a constant All Lucky 7's status).