If you are 75% good, your counterpart will be 75% evil.
If you are 99% good, your counterpart will be 99% evil.
What do you do if you meet your evil counterpart?
If you are 75% good, your counterpart will be 75% evil.
If you are 99% good, your counterpart will be 99% evil.
What do you do if you meet your evil counterpart?
Killing villains doesn’t make you evil. Unless you were already evil which would make your counterpart good, and killing them is just in your horrible nature.