The research team (Damisch et al. (2010) had the idea that having a lucky mascot might actually improve confidence, and therefore performance. So they ran some experiments including one where participants could bring their lucky mascot or charm with them do do a test. Before the test the items* were taken away to be photographed. One group then had their mascots returned, the other group were told the mascots would be returned after the task. The former group did better in the memory task and further tests showed this was linked to an increase in self-confidence. This link would seem to apply also to self-esteem, attribution of success and self-belief.
So maybe if you do have your own lucky mascot it could be a good idea to keep it by you when you are competing or doing exams.
* from old stuffed animals, and stones to wedding rings