The universe is uncannily balanced and I think that any immediate change in anything would have horrific results.

Could you elaborate on why you think this? Because I do doubt that there'd be any problem caused by one small change on one world.

The problem is that how do we know Oddworld has the same Gases then Earth, we might not be able to breath.

As we're talking hypothetically, all that doesn't matter. As Bullet Magnet once brought up, looking at the mass of the planet and what have you, it's impossible for the inhabitants to be as they are, so obviously, real science doesn't apply on Oddworld.

With just the fact that there is gases, we would still be able to breath. We can breath every gas (air is a mixture of gases) because our lungs are designed to take in gases - some of which are lethal. Our bodies may not use some of the gases but are still breathed in. I'm not been a dick, I'm just pointing out :).
Anyways, the vital gases on Oddworld though, may not have the same effect to our bodies as oxygen but the inhabitants bodies may be adapted to an oxygen-like gas that our bodies wouldn't 'know' how to use.
On the other hand, Oddworld looks to have some of the same plants Earth has. This means that they may respire with carbon dioxide then excrete oxygen.
Yet again, the Oddworldian plants may just be used to using a carbon dioxide-like gas for photosynthesis and excreting a oxygen-like gas.

Either way, we'd still be Scrab chow :P

(Wasn't the guy who made this thread just on some really stupid revenge mission?)

Yes. Yes he was. He was such a dick.

I have nothing else value to contribute to this thread now. Sorry.