Hm... it depends. If I had a twin, and they were identical, I might try to pull a trick some friends of mine used to pull in school. Back in elementary school, we had a set of twins, one of which that was really good in math and science, and another that was really good in English and Social Studies. So before tests, they'd switch places because no one could tell them apart. They always wore the same clothes and the only way to know which was which was their shoes, but they'd switch shoes too just to be sure. I would hope my twin is good at math and science and then we could switch places. XD

If they were fraternal, I'd just hope they'd be a close friend that always has my back. When I was a kid the main reason I wanted a sibling was because it was lonely to play Smash Bros by myself. But if I had a twin, I would never have to play games alone again! Plus, if they were a guy, they could be my wingman! Or something.