After some teasing of undiscovered secrets by producer Mark Warburton on Twitter, LEGO community members have discovered four appearances of Doug Rattmann in Portal test chambers. Rattmann is a character who doesn’t make an appearance in Portal or Portal 2, but his handiwork can be found scribbled on walls in both games.
For the Portal levels in LEGO Dimensions however, players have found his minifigure makes an appearance in Test Chambers 02, 06, 07, and 09. To find glimpses of him, players will need both a flying vehicle with speed boost and Chell. When discovered Rattmann will drop studs or a heart. You can watch the explanations for how to find him in the video below.