Update 3

command /ban [<offline player>] [<text>]:
  description: Ban the naughty people!
  usage: /ban <player> <reason>
  permission: skript.ban
  permission message: &cYou do not have permission to use this command!
  trigger:
    if arg 1 is not set:
      send "&cPlease specify a player." to player
    else if arg 2 is not set:
      send "&cPlease specify a reason." to player
    else if {ban.%arg 1%} is true:
      send "&cPlayer is already banned." to player
    else if {ban.%arg 1%} is not set:
      send "&cThis player has not even joined the server!" to player
    else:
      broadcast "&b%arg 1% &7was banned for &b%arg 2%&7 by &b%player%&7."
      ban arg 1 by ip
      set {banned.%arg 1%} to true

command /unban [<offline player>]:
  description: Forgive the punished!
  usage: /unban <player>
  permission: skript.unban
  permission message: &cYou do not have permission to use this command!
  trigger:
    if arg 1 is not set:
      send "&cPlease specify a player." to player
    else if {ban.%arg 1%} is false:
      send "&cPlayer is not currently banned."
    else if {ban.%arg 1%} is not set:
      send "&cThis player has not even joined the server!" to player
    else:
      broadcast "&b%arg 1% &7has been unbanned by &b%player%&7."
      unban arg 1 by ip

command /mute [<offline player>] [<text>]:
  description: Mute the naughty!
  usage: /mute <player> <reason>
  permission: skript.mute
  permission message: &cYou do not have permission to use this command!
  trigger:
    if arg 1 is not set:
      send "&cPlease specify a player." to player
    else if arg 2 is not set:
      send "&cPlease specify a reason." to player
    else if {mute.%arg 1%} is true:
      send "&cPlayer is already muted." to player
    else:
      broadcast "&b%arg 1% &7has been muted for &b%arg 2% &7by &b%player%&7."
      set {mute.%arg 1%} to true

command /unmute [<offline player>]:
  description: Give voice to those who cannot speak!
  usage: /unmute <player>
  permission: skript.unmute
  permission message: &cYou do not have permission to use this command!
  trigger:
    if arg 1 is not set:
      send "&cPlease specify a player." to player
    else if {mute.%arg 1%} is false:
      send "&cPlayer is not currently banned." to player
    else if {mute.%arg 1%} is not set:
      send "&cThis player has not even joined the server!" to player
    else:
      broadcast "&b%arg 1% &7has been unmuted by &b%player%&7."
      set {mute.%arg 1%} to false

command /warn [<offline player>] [<text>]:
  description: Warn the naughty!
  usage: /warn <player> <reason>
  permission: skript.warn
  permission message: &cYou do not have permission to use this command!
  trigger:
    if arg 1 is not set:
      send "&cPlease specify a player." to player
    else if arg 2 is not set:
      send "&cPlease specify a reason." to player
    else if {mute.%arg 1%} is true:
      send "&cPlayer is already muted. (Cannot get more warns)" to player
    else if {mute.%arg 1%} is not set:
      send "&cThis player has not even joined the server!" to player
    else:
      broadcast "&b%arg 1% &7has been warned for &b%arg 2% &7by &b%player%&7."
      add 1 to {warn.%arg 1%}
      if {warn.%arg 1%} is 3:
        broadcast "&b%arg 1% &7has been automatically muted for &breaching three warns&7."
        set {mute.%arg 1%} to true
        delete {warn.%arg 1%}

command /kick [<offline player>] [<text>]:
  description: Kick the naughty!
  usage: /kick <player> <reason>
  permission: skript.kick
  permission message: &cYou do not have permission to use this command!
  trigger:
    if arg 1 is not set:
      send "&cPlease specify a player." to player
    else if arg 2 is not set:
      send "&cPlease specify a reason." to player
    else:
      broadcast "&b%arg 1% &7has been kicked for &b%arg 2% &7by &b%player%&7."
      kick arg 1

on chat:
  if {mute.%player%} is true:
    cancel event
    send "&cYou were a naughty boy and as a result you have lost your permission to talk." to player
  else:
    stop