Yeah, I'm just confused why it isn't in any of the video descriptions like it usually is. I just looked at the Elder Scrolls and Avowed one-shots, which were done at a similar time to the Assassin's Creed one. The art for both of those was done by Julie Dillon, and the art style is also similar. It's very possible that due to those details it was done by them, but there is no confirmation.
I looked and haven't found the official artist, which is strange because Critical Role will usually credit them. My theory is that the artist was commissioned by Ubisoft, and they paid an additional fee so the art didn't have to be credited. I could obviously be wrong, as I haven't watched the one-shot, but I don't think they were publicly credited.
I think that the fact that she is a follower of Sarenrae makes a difference in this scenario. In the lore we have about Sarenrae and her relationship with Asmodeus and the goal of redemption Zerxus can be compared to her. Also consider that this didn't happen in campaign and it might not make sense for her to lose her class feature right before a major plot point.