According to Valve writer Chet Faliszek, there was once competitive multiplayer in Portal 2.
Just about everyone loved Portal 2's co-operative multiplayer, but according to Faliszek, who spoke at Valve's GDC 2012 Portal 2 post-mortem panel, few would have liked the competitive version.
“We had a competitive multiplayer set at one point, but it was no fun and hard to tell what was going on," Faliszek said. "Luckily we cut it very early on and were able to put our resources elsewhere.”
In fact, early stages of Portal 2 were nothing like the game we ended up playing. Valve basically tore the entire Portal concept apart, and at various times, removed everything that made the game recognizable, including the setting, main characters and gameplay.
“We cut Chell...We cut GlaDOS”...We cut portals," Faliszek and his fellow Valve writer Erik Wolpaw said.
“In F-Stop Portal 2 [the original iteration of Portal 2], Cave Johnson was the main character. He was a southern Billionaire but eventually transitioned into the midwest millionaire he was in Portal 2," Wolpaw said. “GlaDOS was gone and we only had her in as Betty, a small robot that would roll out and give the legal guidelines to the player before each test.”
Eventually, the things that made Portal the game we know were added back in, but one part of the first game was not put into Portal 2.
“Still cut was the cake, and nobody missed it," Wolpaw said.