For years fans have been enjoying the full-blown Mega Mani OVA "The Day of Sigma," a 24-minute feature that sets the stage for the Mega Man X series. It isn't distributed all that often from Capcom, but that might change based on a BBFC classification that contends that the Mega Man X Legacy Collection (either its single or dual release, we're not sure) will include it.
Right there in the listing, which includes a rundown of the extras menu (and mostly consists of various trailers for Mega Man X-X8), is Day of Sigma in all of its 24 and a half minute glory. Now you have a choice: you can either wait for the X Legacy Collection to maybe include it, or just watch it below on YouTube, where it's been available for the last five years by way of its inclusion in Mega Man: Maverick Hunter X.
When I said "elusive" I mean that in the official sense!
Mega Man X Legacy Collection [BBFC via Rockman Corner]
via destructoid https://www.destructoid.com/elusive-day-of-sigma-ova-might-be-included-in-upcoming-mega-man-x-legacy-collection-495990.phtml