if you want to make the same modifications:
the level: https://mb.srb2.org/addons/sonic-robo-blast-2-the-past-version-2-0.4613/
the sonic version: https://mb.srb2.org/addons/past-trio.5603/
the HUD: https://srb2workshop.org/resources/halloween-doom-legacy-styled-hud.440/
I found SRB2 in the final 1.9.4 (or something like that) demo around 2009 and don’t remember this. Early indeed, crazy how long the community has loved on this work.