Mutation or what?

I think the twin is essentially dead already. You will hopefully be left with one, healthy plant. I would do nothing now as you risk doing more harm than good. Over the next few days the one sprout will die and dry while the other will grow stronger. The growing plant will naturally shed the dead sprout or it will just be lightly hanging off the healthy plant causing no harm. Either way just wait a week and you can remove the second plant without risk of hurting the healthy plant.