Motif Merger

A Motif Merger is a stylistic 'beat' sometimes used during a crossover. It's when both 'sides' have certain things that are their trademarks, and (during the crossover) there's a symbolic moment where the two motifs are either swapped or combined.

Comic Books

 * The logo for DC's current Superman/Batman series is Superman's shield logo inside a bat logo.
 * The logo for the Trinity series combined Superman, Batman, and Wonder Woman's symbols.
 * Devils Due's G.I. Joe VS Transformers used a mash-up between the Cobra and Decepticon symbols in advertisements, but not in the actual comic (except to separate issues in the collected edition)

Film

 * The movie Freddy vs. Jason had a moment of mixing icons: a slow pan down from tree level, coming down onto a sign reading "Elm Street", while the soundtrack played the Friday the 13th "ki-ki-ki-ki, ma-ma-ma-ma" leitmotif.

Live Action TV

 * The shows Homicide: Life on the Street and Law & Order, which had distinctive ways of sequeing from one scene to another, crossed over once. During the crossover, the scenes in New York [L&O's turf] were filmed with Homicide's transitions, and those in Baltimore [Homicide's setting] had L&O's transitions. (That is: Cut to black, glun-glung, text: "Baltimore Homicide Division, 10:30 AM.", fade in.)
 * Quite common in Super Sentai teamups, with the team's logos merging. For example, Juken Sentai Gekiranger vs Engine Sentai Go-onger ends with the Geki triple-claw emblem on top of the Go-onger "G" speedometer.

Professional Wrestling

 * Sometimes two wrestlers forming a tag team will have their respective theme tunes and entrances "mashed up". Examples: Luger & Smith, the Allied Powers; Kane and Hurricane Helms as HurriKane, or the Corporate Ministry (The Undertaker's "Ministry of Darkness" and Vince McMahon's "Corporation" stables, merged) using a remix of the Corporation's theme in the style of the Ministry's theme.

Videogames

 * Sonic the Hedgehog 2006: Mephiles has a sinister-sounding piano Leitmotif (with a techno remix as his boss fight music). Iblis is accompanied by a bombastic, orchestral score. When the two fuse together to form the True Final Boss Solaris, the phase 1 boss music is Mephiles' leitmotif, performed by Iblis' bombastic orchestra.

Web Original

 * Todd in the Shadows uses this whenever crossing over with other reviewers from That Guy With The Glasses .com. For example, he plays Film Brain's "Ready to Roll" theme, in the style of his "Playing today's song simply, on a keyboard" routine, and his 'similar-theme, but way better-done' bit over the credits of his review of "It Wasn't Me" with The Rap Critic (Todd chooses Mozart's "Cosi Fan Tutte" (lit. "Everyone's Doing It"). )

Western Animation

 * In the animated DCAU crossover movie "World's Finest", the Bat-Signal (Batman's emblem) is broadcast onto the globe on top of the Daily Planet Building (Superman's).
 * The exact logo at the top of the page also appears in "Superman/Batman: Public Enemies"
 * The crossover between Ben 10 Ultimate Alien and Generator Rex, Heroes United, had Ben 10's Omnitrix at the center of Rex's gear logo.
 * Similar to the above, the crossover of The Grim Adventures of Billy and Mandy and The Kids Next Door has the openings combined, making the KND operatives grow flesh from bone like the former's opening.

Real Life

 * Quite common with national flags and coats of arms.
 * The Union Jack was originally a combination of the flags of England and Scotland. Later, Ireland was added.
 * But not Wales.
 * Wales was invaded. The others joined peacefully, but a few problems arose.