Adaptation Sequence: The Scorpion King 2 might just take the cake. It's a direct to DVD prequel of a spin-off of a sequel of a remake.
California Doubling: More like Arizona Doubling with The Scorpion King, the one of the series (so far) entirely filmed in the US (the sequels went for South Africa, Thailand and Romania).
Fake Nationality: Samoan American Dwayne Johnson as Akkadian Mathayus in the first film. Filipino American Michael Copon in the second film and Canadian Victor Webster in the third and fourth films.
The Other Darrin: Michael Copon replacing Dwayne Johnson in the second film. Justified since the second film is a prequel. Played straight with Victor Webster for the third and fourth films.
What Could Have Been...: The first movie's DVD includes alternate versions of several scenes showcasing an entire prophesy plot that was cut. Said plot explained the villain's whole motivation and the otherwise confusing ending.