Portal was a singleplayer game. Portal 2 adds co-op, but did you know it was at one stage also going to add competitive multiplayer?
"Along with co-op, [we had]the idea of sort of a competitive Portal multiplayer," Valve's Erik "Old Man Murray" Wolpaw told 1UP.
"We went down that path, actually, for a little while and had something up and running - the best way to describe it is sort of Speedball meets Portal. You know, a sports analogy. And it quickly became apparent that while it's fun for about two seconds to drop portals under people and things like that, it quickly just devolves into pure chaos. It lost a lot of the stuff that was really entertaining about Portal, which was puzzle-solving. Cooperative puzzle-solving was just a much more rewarding path."
Wolpaw says this game mode, which had you shifting a ball around, was a "hot mess".
Speedball meets Portal was a bad thing? Just goes to show, dreams don't always come true.