That’s not what I would call “manifestation,” that’s black magic. Which, needless to say, nobody should ever engage in.
I believe that causing other people harm will ultimately come back to haunt you and destroy your soul (aka, put you squarely into the territory of the “Dark Side”).
Even if you “only” wish something terrible to happen to someone (vs. actively doing something to harm a person), it’s an act of evil. Leave the punishment for bad deeds up to God… and remember that the Bible tells us to pray for our enemies. So if you want to accumulate brownie points for Heaven, try some heartfelt prayer asking God to help the evildoers recognize the error of their ways so they can be saved.
If the evildoers did something to you personally, forgiveness is even more important. After all, it's really mostly for your own sake, not for the other person’s, because hatred will eat you from the inside. Forgiveness, on the other hand, can do wonders for you in terms of stress relief and peace of mind.
Try the Goodwill Manifestation to spread blessings to everyone you meet… even to unpleasant people. It’s a very simple technique, and you’ll see amazing things happen.