Half Life 2: Portal

http://www.youtube.com/watch?v=gKg3TUPQ8Sg

Quote:

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So you’ve played through Portal and loved every minute as much as we did. Maybe you’ve even gone through the advanced maps and tried out some of the challenges? So what comes next?

How about the ability to play through Half-Life 2, HL2 Episodes, or other Source-powered games with the portal gun in-hand? We’ve been doing that very thing for the past few days now, and after hours spent experimenting with various techniques and tricks, we’re here to show you how.

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Have a look here to find out how to do this.

NOTE: You need Portal and HL2 for this to work.

Nice, that adds the whole new challenge of using weapons through portals, since Portal doesn't have any weapons. Anyway, Aperture Science which made the portal gun are in the same 'Universe' as Half-life 2, since they're rivals to Black Mesa, and Aperture Science is even mentioned in episode 2, and involved even more in episode 3. So it's most likely that the portal gun will be in episode 3 anyway.