Legolas-mode is enabled by quattro-heirlooming a hunting bow and using a special ALT-X cheatcode in game...
errr - not. ;-)
Actually I do not know. I have occasionally seen very fast archers - some seem to use Khergit-Bow (heirloomed), which is way faster than strongbow, warbow or the crippled longbow anyways. Heirlooming it makes it even faster (even my warbow has become a bit less clumsy in the meantime). Combine that with high WPF and a lot of points in agility - might have that result.
On the other hand: unless they go for headshots these guys are more a pain in the butt than effective, since even I as an archer, usually wearing a pilgrim outfit, can take several of their arrows before going down.
So not an archer mode for me. When an arrow hits, the target should not squeak and start jumping, but say *fump* and go down.