In the Boss Fight Event, five players battle one player's "Boss" Brawler. The Boss has very high health, improved damage output, and enhanced abilities, but their ability to self-heal is removed. Instead, The Boss has a health decay that removes a couple hundred health every second. The Boss attempts to stay alive for as long as possible while the others try to defeat the Boss as quickly as possible. The time on the clock when the Boss is defeated determines how many Keys the participants receive. The Boss "wins" the mode by surviving past 2 minutes and 5 seconds, for which they receive the most Keys. Likewise, the normal players win by defeating the Boss in under 2 minutes and 5 seconds. Because of the health decay, the maximum survival time of The Boss if they were not to be damaged at all by the opposing team would be about 5 minutes. This is an unranked mode, so Trophies cannot be earned or lost.
- Darryl and Bull: These Brawlers can use their Supers to escape from large groups of Brawlers.
- Spike: This Brawler's Super is amazing against the Boss since it slows them down significantly, allowing the group to get many hits on the Boss.
- Mortis: The Boss's reload speed is greatly increased in this gamemode. Because of this, Mortis as the boss would be able to escape bad situations and kite the opposing team for a long time with his dash. He can also damage a few Brawlers in the process.
- Jessie and Nita: Both of these Brawlers are useful because their Supers spawn either a turret or a Bear. Both have greatly increased damage and health, and it can be useful for taking out opponents or distracting them for you to take as minimal damage as possible.
- Bosses can get more Keys the longer they stay alive. Instead of fighting, you can simply run away from enemies to last longer.
- Attack the Boss from all sides in order to overwhelm them.
- If the Boss is a single-target attacker, try to attack them all at once. If you just send Brawlers in one at a time, the Boss will be able to pick off the individual Brawlers more easily and survive longer.