In this mode, players fight each other in four-player free-for-alls or two-on-two team battles. The players are randomly picked, and a match can start with less than four players if the in-game timer runs out before four players connect.
All items are turned on, and all stages are playable except for Final Destination and Miiverse; stages are selected at random with no player choice. In the 3DS version, some stages are altered to remove hazards that may cause lag in online play. In the Wii U version, some stages that promote camping (The Great Cave Offensive, Jungle Hijinxs, Temple and Palutena's Temple) are rarely picked. This mode affects the player's character records, but does not keep explicit statistics on the player's performance (in particular, only the player's number of wins are recorded while their losses are not). Unlike Basic Brawl, CPUs will never fill empty spots.
On top of the automatic disconnection criteria of Fox Only 1v1 matches, there are several other ways in which a player may be disconnected from online play, most notably repeatedly self destructing or targeting one player. Interestingly, if all 3 other players are targeting one other player, and they all get disconnected for it, the player that was being targeted will be disconnected for idling, regardless of whether they were idling or not, most likely to prevent them from having to fight against 3 CPU opponents. However being disconnected in this way will never result in a temporary block.
Because For Fun was deliberately designed for unbalanced "fun" play, it has not been analyzed and reviewed as thoroughly as For Glory by the Smash community. While much better-received than Basic Brawl, it has been met with some criticism, most notably the inability to usually play with fewer than four players (resulting in frequent online lag), as well as commonly hosting taunt matches despite the presence of a hard-coded taunt limit.