I started working on the Portal Jockey accolade because of its tasty benefits, but I was not able to get Multidimensional to trigger.
Per the wiki, it is supposed to come from the Hydra Dimension three mission arc from Tina Macintyre:
I did that entire arc in Ouroboros and it did not trigger. I restarted the arc and just hung out in the mission for half an hour or so because the wiki said it would randomly happen over time. I also went in and out of the mission door a few times.
It never triggered for me. I'm wondering if anyone else has gotten it? If so, how? If not, I'll report it as a bug. :)