Getting Odin in Final Fantasy 7 is very easy. It requires you to be in Shinra a second time. The first time, of course, in the flashback in the city of Kalm when you first leave Midgar.
Once you enter the Mansion, there are 4 clues scattered everywhere. Each one will give you a hint of the safe combination that is above. If you want to know each clue and where to find each one, you are probably reading the wrong article. I’m just going to cover the actual combination itself. To get to the safe, enter the mansion and go up the stairs. Now head left and then go up to the north room. The safe is against the wall.
Don’t miss a number or it won’t work. The combination is Right 36, Left 10, Right 59, Right 97.
After entering the combination, you will automatically get into a fight with a boss named Lost Number. It is made up of 2 monsters, a red side and a blue side. The red side casts magic and is obviously very resistant to your spells. The blue side only attacks physically and is of course resistant to physical attacks. The boss will turn into a single monster after a certain amount of damage. Which side, blue or red, depends on what kind of attack yours made the last blow. A physical attack will give you the blue monster and a magic attack will give you the red one.
The easiest way to kill this monster is to hit it with summons and magic. Boundary breaks will also help a lot. This will cause it to turn into a red monster that is highly vulnerable to physical attacks, so all you have to do is hold down the circle and observe your party’s health.
After the victory, you will find a red ball on the ground. This is Odin’s Summoning Materia. Pick it up and it’s yours. Now you can summon Odin in any battle.