MAA GB
Since davmaha posted a few cool stuff here is how to make it work:
1. Download XML files and open Charles:
https://mega.nz/#F!9MFixIAC!42VTrj_vl9q0UjRbbjJUTA
2. Go to Tools/Rewrite
3. Enable and import the two XML
The one GroupBoss.xml makes your group boss on mission map to be playable many times (you can kill him over and over again)
The BossesFromFriends.xml makes your friends group bosses appear on your ally bar
update: do not defeat old bosses, after refresh everything is lost.
Repeat after me