This wording is backwards: Which rewrites .com/game.php?game=34 to .com/arena/MW2. Its the other way around, the path /arena/mw2 is mapped to /game.php?game=mw2.
You don't need to do a thing. The rule you have will still match the MW3 as your rule specifies it must end in /arena/(.*) which it does. You only need to alter the pattern if you need to capture which platform it is on.
This wording is backwards: Which rewrites .com/game.php?game=34 to .com/arena/MW2. Its the other way around, the path /arena/mw2 is mapped to /game.php?game=mw2.
You don't need to do a thing. The rule you have will still match the MW3 as your rule specifies it must end in /arena/(.*) which it does. You only need to alter the pattern if you need to capture which platform it is on.
When i go to /platform/360/arena/mw3
it just takes me to the platform.php file not the game.php (arena) file
And that's correct. Your platform rule matches your input prior to your arena check.
You can either refine the rulesets, or you can move the check for arena up and flag it last with [L]
Edit:
Wait, your rules have changed. You'll need to write a more refined rule if you plan on adding a starts with to the pattern.