Perfect Play-through

[Sephiroth]

Indeed. And Vincent's ultimate weapon has to glitch for a perfect save data.

What does that mean?

In case you get Vincent's damage high enough with his ultimate weapon because you have beaten 65535 enemies Final Fantasy VII is confused because of the damage calculation and the high stats. You don't even have to beat 65535 monsters. It is enough to beat very, very much and use a lot of Hero Drinks. Than the Death Penalty glitches and when you attack your enemy, Final Fantasy VII says something like "||||" instead of "9999" and your enemy - no matter if Ruby WEAPON, Emerald WEAPON, Safer Sephiroth or everyone else is automatically defeated.

So for the perfect save data I mean you have to beat 65535 enemies of course. It is the maximum to count. But then his ultimate weapon will definitely glitch.

And Vincent is not the only one. Barret's Missing Score has the same glitch as well. Just use a lot of MASTER materia and Hero Drinks - but Barret's weapon glitch is not necessary for a ultimate save data because his weapon damage is not calculated by beating monsters so it does not matter if you beat 65535 monsters with him. His glitch will only happen with all these materia and the strength increasing Hero Drink items.