Nice idea. Although a plugin wouldn't be my first choice as it has has its limits. eg:
The stats: They need to be syncronized each time with all the contacts that have the same battle, etc...
Also you're limited to your personal contactlist (unless some of your contacts invite another person from their contactlist, but the sync-problem still remains).
There is also maybe a privacy issue involved.
Maybe this could much better be made as a bot which you need to add as a contact.
just a suggestion
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