Chaotic Greedy
Speaking of crossover, it amuses me that since the latest Stellaris patch, you actually build your ships out of "alloys". Which would clearly be alien alloys to any pre-FTL civilization you meet.
Huh, I was somehow under the impression that Tactical Analysis was such a good continental bonus that it was only allowed for non-two-territory continents, but lo and behold there it is in Australia for my latest campaign.
And on the topic of crossovers... so back in my third War of the Chosen campaign, I wound up with more Rookies than I needed, got bored, and dressed a Japanese soldier up in a black Reaper trench coat, gave him the callsign "Chuuni." Wound up becoming an ironic/non-indicative nickname when he became a Psi Operative later on. Anyway, fast-forward to now when I'm doing one last campaign before uninstalling to clear up space on my hard drive, and early on Yoshio "Chuuni" Kato (re)joins XCOM as a mission reward. I have a chuckle and stick him in the training school just to give him his starting perks (I'm using the highly-recommended Mushashi RPG Overhaul), then put him on the bench so I can continue to develop my A and B teams.
But then comes tonight's Retaliation mission, and between fatigue and covert ops, I'm short on quality soldiers. I do what I can but there's still a spare slot on the Skyranger some hapless Squaddie is going to have to fill, and when I check over the bench-warmers I notice that Chuuni has a genius intellect thanks to his RPG perk, so between that and starting with the Templar's AP-boosting Resistance Order, if I level the guy, Chuuni is gonna be a beast! Then I notice that I've got some promising Sentinels and Riflemen and Assaults and one hell of a Sniper, but no one innately suited to be my favorite class, Ranger. And then I have to have a good cackle when I realize I'm giving an Arc Blade to a Japanese kid in a black duster in hopes of turning him into an OP swordmaster.
(if it makes you feel better, I only got into it through the abridged series)
When XCOM goes absolutely nuts on the ADVENT Forge
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And surprisingly, a Borderlands sorta-crossover short story to accompany it in the comments.