Anyone who has seen any tidbit of gameplay from Ubisoft's Mario + Rabbids: Kingdom Battle knows, hands down, that the game looks like it has some sort of roots in XCOM. Well, unsurprisingly, the team working on Mario + Rabbids actually sought out the creator of the original X-Com from way back in the 1990s.
According to PCGamesN, Julian Gollop, one of the original creators of Micropose's X-Com, was apparently asked by the team at Ubisoft if he could lend a hand on Mario + Rabbids: Kingdom Battle. However, they couldn't tell him what they were working on exactly and had to be coy about the project, with Gollop recalling how the event played out, telling PCGamesN...
I didn't know at the time that the project he was talking about was Mario + Rabbids, he couldn't say what it was. Nevertheless, had I been at Ubisoft I may have worked on it.
For a little extra context, Gollop was actually working at Ubisoft for a spell, and creative director Davide Soliani had sought out Gollop to work on the title with the rest of the team. However, given that the team was under strict NDA not to actually talk about what they were working on, Soliani was unable to inform Gollop that Ubisoft had landed a lucrative license to use Nintendo's Mario brand.
Gollop had actually departed from Ubisoft during the time when Soliani and the crew were neck deep in developing Mario + Rabbids. Gollop had moved on to work on Phoenix Point, which is an X-Com successor of sorts.
The current brand of Gollop's original franchise is now handled by 2K Games and Firaxis, with a slight tweak to the title so that the game now goes by XCOM instead of X-Com (no more hyphen and all caps).
It makes absolute sense that Soliani would want Gollop on the project because Ubisoft was given explicit instructions from Shigeru Miyamoto that it could make a Super Mario game so long as it was not a platforming game. Ubisoft then had to brainstorm what to come up with that would make sense for the Super Mario brand while not being a platforming game (and obviously not a Mario Kart clone). The team also had to avoid anything out of character, such as a first-person shooter, or an ultra-violent game. Soliani and the crew ended up settling with the turn-based strategy genre, which managed to become a big hit among critics.
However, one could only imagine how much more the game might have changed with Gollop offering some kind of direction and guidance on the project.
Even still, Gollop praised Soliani and the rest of the crew at Ubisoft, saying that despite it being in an "unusual" setting it is also "brilliant". Gamers and critics seem to agree.