-If your HP is exactly 7777, you will attack random enemies numerous times doing 7777 damage. To reach that number of HP, get your HP to be 1 at end of a battle. Then, have a character with 184 magic cast 3 Cures on that character. Note: That character's HP will drop down to 1 afterwards.
-Another way to get 7777 fever is to get your player's HP below 154, then use the Cait Sith's Bell to get your HP to 154. Use Demi2 and half your HP to 77. Then, use curative items (not magic), to get your HP to 7777. After the battle, repeat the process.
-Note: This trick requires the Hp<>Mp Materia, at least 13 Hi-Potions and 4 Potions. First, get to level 99 with Cloud. Check his MP. It should be 877, with no Materia equipped. Use a couple Ethers to get his MP full. Equip the Hp<>Mp Materia to Cloud then unequip it. If done correctly, his HP should be at 877. Use 13 Hi-Potions to get his HP to 7377. Use the four normal potions to get his HP to 7777. You can do this as many times as desired, because Cloud will not gain more MP as he is already on level 99.
-Get the Enemy Skill Chocobuckle, then run from battle 2222 times so that Chocobuckle inflicts 2222 damage. Use it on a character with 9999 HP to get All 7s Fever.
-If you are close 7777 Fever (for example, if your HP is about 7780), change your enemy (or enemies) into frogs or mini. Each time an enemy attacks you, it will only do 1 HP worth of damage. Wait until your HP reaches 7777 and unleash it on your enemies.