As battleground Kumas Royale has no location in open world and is only accessible using Battleground Matching dialog.
In Kumas Royale, all players are transformed into kumases and battle it out for victory over three rounds. One player in team can and should take big kumas or Mama Kumas who is more powerful, but whose survival also means victory in match. Small kumases or "babies" respawn after few seconds in team base.
Battleground was released in June 2016 (NA Aces Wild patch, EU Tricks & Treachery) Battleground was originally 10 vs 10. Later matchmaking was changed so that players below level 65 and level 65 players had separate queue. This totally killed BG for level 65 players.
Queues were combined again in January 2019 PVP patch and also level 65+ player can play the BG. BG was changed to 5 vs 5 with lowered HP on bosses.
Kill enemy Mama Kumas. The team whose Kumas boss has more HP left at end of timer wins the round. Two wins are needed to win the match.