<?php
$weapons = ['fists', 'whip', 'gun'];
$opponentWeapon = $weapons[rand(0,2)];

switch ($opponentWeapon){
    case 'fists':
        $indyWeapon = 'gun';
        break;
    case 'whip' :
        $indyWeapon = 'fist';
        break;
    case 'gun' :
        $indyWeapon = 'whip';
        break;
}
echo 'Opponent weapon is : '. $opponentWeapon . '<br/>';
echo 'Indy weapon is : '. $indyWeapon;