The unicorn footage is definitely NOT from Legend, although it is easy to see why the rumor is so persistent, as the imagery looks quite a lot like that of "Legend".

Despite what many seem to believe, original unicorn footage was in fact shot for the 1982 release; however, at the request of the producers (who didn't "get it", or just decided it was "too arty") it was cut.

When plans were made to make a DC, Scott insisted the footage be reinserted. Unfortunately, by that time, the intended unicorn footage had disappeared. However, one particular shot - an out-take from the original footage that had been discarded by Ridley Scott in 1982 - was found. That shot was cleaned up and colour-corrected, and became that particular BR scene we all know and love... ;-)

[- Source: Future Noir, page 366]

Note: A considerable amount of original footage was rediscovered when preparing to make the Blade Runner Special Edition. It is quite possible therefore that we may yet see more of the original unicorn sequence!

Can you tell me how to make my own origami unicorn?

No, but Shigeki Hayashi can! Visit his site for detailed instructions on how to fold the unicorn.