Gym Wars 2: Feebas Unleashed is a Pixelmon sidemod that allows servers to create and set up Pokémon Gyms with their own players as Leaders.

Installation :
Gym Wars 2: Feebas Unleashed is currently incompatible with the latest version of Pixelmon. It was last compatible with Pixelmon 5.0.1. Another Gym Plugin is an alternative Gym plugin that can be used for the latest Pixelmon versions.

Gym Wars 2: Feebas Unleashed only needs to be installed on a server and does not require each player to install it in order to be used.

Minecraft launcher
Download Gym Wars 2: Feebas Unleashed for your version of Minecraft here.
Place the downloaded file in the mods folder.
Pixelmon launcher
Edit your profile and choose the "Add Official Sidemod" option.
Select Gym Wars 2: Feebas Unleashed from the list.
Commands
Note: Command syntax is displayed in the standard Minecraft command format. An explanation of this format can be found here.

/acceptchallenge <Gym>: Accepts a Gym challenge which will teleport both players to the Gym and start the battle.
/addleader <player> <Gym>: Adds a player as a Leader of the specified Gym.
/badge <give|take> <player> <Gym>: Admin command for giving or taking Badges from a player.
/badges [player]: Opens the inventory containing the Badges of the specified player, or the command user if no player is specified.
/challenge <Gym>: Sends a challenge request to the Gym for a Leader of that Gym to accept. If there are other challengers, the player will be put into a queue to wait until the Leader completes all previous challenges.
/cancelchallenge <Gym>: If a challenger wants to cancel a challenge before it is accepted, this command will remove the challenger from the queue of challengers.
/creategym <Gym name> <type> <level cap> <Badge> <battletype> [order]: Creates a Gym with all of the properties specified.
Gym name: The name of the Gym to be created. No two Gyms can have the same name.
type: The type of the Gym which the Leader's party Pokémon must contain for a Gym battle.
level cap: The highest level that either the challenger's or Leader's party Pokémon may be for a Gym battle.
Badge: The Badge that will be rewarded to the player after a victory. Input is the name of the Badge without any spaces; e.g., HeatBadge.
battletype: The type of battle that will occur in the Gym. Either Single or Double.
order: If Gym order is enabled, this defines the order in which Gyms must be challenged.
/deletegym <Gym>: Deletes a Gym and all of its properties from the server.
/editgym <Gym> <property> <value>: Edits a certain property of the specified Gym. The value argument is the new value of the specified property. The properties that can be edited are as follows:
name: The name of the Gym.
type: The type of the Gym.
levelcap: The highest possible level that a Pokémon can be in a Gym battle.
badge: The Badge awarded by the Gym.
battle-type: The type of battle that will occur in the gym. Either Single or Double.
/gyminfo <Gym>: Gives information on the properties of the Gym specified, including the Gym name, type, level cap, Badge, Gym Leader position, and challenger Gym position.
/gymlist: Lists all Gyms (in order if applicable), their statuses (open or closed), and all online Leaders for each Gym.
/reloadconfig: Reloads the config so a server admin may make live changes without restarting the server.
/removechallenge: Forcefully removes a challenger from the queue of a Gym.
/removeleader <player> <Gym>: Removes a player from being a Leader of the specified Gym.
/setgympos <Gym> <Leader|challenger>: Sets the position for the challenger/Leader of the specified Gym which they will be teleported to before a Gym battle begins.
/viewchallenges <Gym>: Displays a list of all challengers and the order in the queue they're in.
Permission nodes
/acceptchallenge: feebasunleashed.command.acceptchallenge
/addleader: feebasunleashed.command.addleader
/badge: feebasunleashed.command.badge
/badges: feebasunleashed.command.badges
Allow the user to use /badges on other players: feebasunleashed.command.badges.other
/challenge: feebasunleashed.command.challenge
/cancelchallenge: feebasunleashed.command.cancelchallenge
/creategym: feebasunleashed.command.creategym
/deletegym: feebasunleashed.command.deletegym
/editgym: feebasunleashed.command.editgym
/gyminfo: feebasunleashed.command.gyminfo
/gymlist: feebasunleashed.command.gymlist
/reloadconfig: feebasunleashed.command.reloadconfig
/removechallenge: feebasunleashed.command.removechallenge
/removeleader: feebasunleashed.command.removeleader
/setgympos: feebasunleashed.command.setgympos
/viewchallenges: feebasunleashed.command.viewchallenges
Config settings
"BannedMoves": The list of moves that are not allowed to be used by either the challenger or the Leader in any Gym battle.
"CooldownTimerEnabled": Enables the cooldown timer so that if a challenger loses, the challenger must wait the amount of time specified in the 'CooldownTime' config value in order to challenge another Gym.
"CooldownTime": The time in minutes a player has to wait after losing a Gym before challenging another.
"GymOrder": Whether or not Gyms have to be challenged in a particular order.
"Commands": The list of commands that will be executed after a Gym battle. There will be two config nodes for commands per gym, one that's executed on challenger victory and one executed on defeat. @challenger or @leader can be used in place of a player name to refer to the challenger or Leader in the command.