Lego Dimensions is a pretty detailed game. There are all sorts of Easter eggs and clever asides referring to each add-on’s source material. You really have to look close to see everything. So close, that a Portal secret wasn’t found in Lego Dimensions until now. It turns out there’s always been a secret character!
In the main Portal series, there’s a scientist called Doug Rattman. If you pay attention to the environments in the game, you can see writings and warnings from the Rat Man. It turns out people going through the Lego Dimensions Portal level pack can use special characters and cars to find him in Testing Chambers 2, 6, 7, and 9.
Here’s the video going over Rat Man’s cameos.
This is such a great surprise. Portal was a game with many secrets, so it only makes sense its Lego Dimensions add-on would offer the same sorts of mysteries. We already knew Rat Man’s den was there, so it only made sense he was somewhere in there.
Source: Disney Dan