I am a nut over unpurchasable/unsellable arts. Mashups, teamups from competing companies. For example, recently on Twitter Todd Nauck posted for a week a bunch of X-Men / Justice League mashups

Nightcrawler + Blue Beetle = NightBeetle https://twitter.com/ToddNauck/status/929045650263588864

Colossus + Captain Marvel = Captain Colossal https://twitter.com/ToddNauck/status/929421008125157376

Storm + Batman = BatStorm https://twitter.com/ToddNauck/status/930140041489162240

Rogue + Martian Manhunter = Martian Roguehunter https://twitter.com/ToddNauck/status/929756019999178752

Rachel Summers/Phoenix + Dr. Fate = The Phoenix Fate https://twitter.com/ToddNauck/status/930851960659443712

Cyclops + Guy Gardner, Green Lantern = Cyke Gardner, the Quartz Lantern (or “Guyclops”) https://twitter.com/ToddNauck/status/930484023507410944