Players must first get Costume Brawl skills to begin brawling with other players. Players enter Costume Brawl by using Enter Costume Brawl or any Costume Brawl skill that can hit a foe. This will give the player the Costume Brawler effect, allowing for free form PvP combat. Players may exit Costume Brawl by using Time Out.
When a player enters Costume Brawl, they are given 15 hit points, which are shown as a stack in the Costume Brawler. Players may inflict damage by removing stacks from Costume Brawler. You will gain a stack of Brawler Score whenever you inflict Brawler Damage on another player. Whenever an opponent inflicts Brawler Damage on you, they will remove one stack. If all stacks of Costume Brawler get removed, the player will be knocked back, come under the effects of Brawler Disabled, and remove any stacks of King of the Costume Brawl. These hit points will regenerate gradually over time if the player remains in Costume Brawl and doesn't take or deal damage.
Reaching a score of 25 Costume Brawler points without being disabled grants a stack of King of the Costume Brawl, progress the costume brawl achievement, and your brawler points will reset. You can gain up to 25 stacks of King of the Costume Brawl, but will still continue to accumulate points afterwards. The King of the Costume Brawl achievement tracks the number of times a players has achieved King of the Costume Brawl.
While most sources of Costume Brawl can be obtained during festival events, such as from costumes and tonics, Costume Brawl can be initiated at any time. The witch's cauldron and Mad King's feast provide inexhaustible sources for Costume Brawl if other players do not have a source to join in themselves.
- Costume Brawler — You've entered a Costume Brawl. Attack other players with skills from toys, bundles, and tonics in this free-for-all.
- Brawler Score — Successful hits against other brawlers. A score of 25 will grant you champion status.
- Brawler Damage — Score a Costume Brawl hit on any brawlers in range.
- King of the Costume Brawl — Achieved a score of 25 without being disabled or leaving the brawl.
- Brawler Disabled — You've taken too many rapid hits. You temporarily cannot brawl or be hit.
- Brawler Protection — Blocks all costume brawl skills.
- Costume Brawl Cripple — Reduces movement speed.
- Costume Brawl Daze — Interrupts and prevents skill usage.
- Costume Brawl Fear — Involuntary retreat; unable to act.
The following achievements are currently obtainable:
|King of the Costume Brawl||Community||15|
| Win 500 costume brawls.
||1-Time Brawl Champion||1|
|3-Time Brawl Champion||0|
|5-Time Brawl Champion||0|
|10-Time Brawl Champion||0|