Bluetracker
Tracks Blizzard employees across various accounts.
Switch Co-Op
I haven't been able to find anything regarding how local co-op on separate systems works. I assume it requires each system to have a copy of the game, but I was wondering if it might be like some 3DS games where only a single copy was needed for multiple systems to be used for local multiplayer. Any confirmation one way or the other?
Nevalistis
Each individual Switch participating requires its own copy of the game. /u/Drevs answer is spot-on. :)