Type !play to start the game.
You will be asked to choose between !door1, !door2 and !door3. Behind one of the doors is a car other two contain goats.
When you've picked a door host will open a door which always contains a goat.
Then you will be asked if you want to !swap from door or !stay to stick with your first choice.

on *:TEXT:*:#: {
  if ($1 = !play) {
    hmake $nick
    hadd $nick prize $r(1,3)
    msg # 12There's 04 $+ 3 doors 12and behind one of these doors is a car!
    msg # 12Make your selection: 04!door1, 04!door2, or 04!door3 $+ 12.
  }
  if ($regex($1,/^!door(1|2|3)$/Si)) && !$hget($nick, door) {
    hadd $nick getDoor $hget($nick, prize) 
    hadd $nick door $regml(1)
    while (($hget($nick, getDoor) = $hget($nick, prize)) || ($hget($nick, getDoor) = $hget($nick, door))) { hadd $nick getDoor $r(1,3) }
    msg # 12Host opens 4door $hget($nick, getDoor) 12and reveals a goat! Do you want to 4!switch 12or 4!stay $+ 12.
  }
  if ($regex($1,/^!s(witch|tay)$/Si)) && !$hget($nick, switch) {
    if ($regml(1) = witch) {
      hadd $nick switch $hget($nick, door)
      while (($hget($nick, switch) = $hget($nick, door)) || ($hget($nick, switch) = $hget($nick, getDoor))) { hadd $nick switch $r(1,3) }
      hadd $nick door $hget($nick, switch)
    }
    msg # 04 $+ $nick 12won a 4 $+ $iif($hget($nick, door) = $hget($nick, prize),CAR,GOAT) 
    hfree $nick
  }
}