VFX Breakdown of scifi short Doppelgänger (2013). Cloning, digitally painting skin, masking etc. Doppelgänger is a Finnish scifi short film depicting unfortunate alien interaction with german soldiers.

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Behind the scenes look at creating the lightsaber decapitation from Jedi Knight, Exile (2012), Star Wars fan film. Step-by-step process should give you rough idea on how the effect was made.