What you want is the Battle Royal Dome page. BP-wise, Battle Royal is slower than a well-orchestrated Mantine Surf run, and compared to using Battle Tree, the potential upside is lower (5 BP per match at best, instead of 7 for a long tree streak) and the matches probably take longer because of the intro and waiting for everyone's actions, but you're assured of at least some BP no matter how badly the match turns.