Battle Royale is an automated RNG battle. The user is prompted to react in order to partake in the battle. These automated fights are timed and summoned by the system.
Unlike Boss Battle, once you enter the Battle Royales, the rest is automated until 1 winner is left standing. No need to interact each round as you do in Boss Battles.
Battle Royale is winner takes all, meaning whoever wins collects all of the payout.
Non-winners can earn 1 stardust for every kill they manage to make in the Battle Royale, but do not get any cut of the final payout if they did not win.
Some NFTs have traits that benefit you in Battle Royale by giving you a better chance at surviving each RNG round.