[StainlessS]

Thanks for taking an interest Mani,
And Yip, it does same in Avisynth v2.60, mvtools2 from mvtools-v2.5.11.22.zip (avs version 2.60 dll dated 26/Apr/2016).

just add Gscript wrapper as this [where not Avs+]

GScript("""
    For(i=1,Steps-1) {
        W=White.Crop(0,0,i*XStep,0)  K=Black.Crop(0,0,Wid-W.Width,0)  Frm=StackHorizontal(K,W) srcS=srcS++Frm
    }
""")

Can you reproduce.

EDIT: I think the first script in post #520 should work as is (with Avs+ OR GScript, and at least version v2.60 standard, +Grid for 2nd script)

EDIT:

Originally Posted by StainlessS

EDIT: I still dont have much clue how that occlusion stuff works.

EDIT: I note that author of YFRC

# Author: RunForLife(Oleg Yushko) http://videomontazh.com.ua
# http://avisynth.nl/index.php/YFRC

uses only backwards Occlusion mask, here posted mod as YFRC2() by RaffRiff42:- https://forum.doom9.org/showthread.php?p=1804170

Below, both SAD masks used, but only BAK backward Occlusion mask.

    ## "EM" - error or artifact mask
    EM  = C.MMask(bak, ml=190, kind=1)   [** kind=SAD *]
    EM  = EM.Overlay(
    \       C.MMask(fwd, ml=190, kind=1).DeleteFrame(0), 
    \       opacity=0.5, mode="lighten")
    
    EM  = EM.Overlay(
    \       C.MMask(bak, ml=64, kind=2).mt_inpand, [** kind=occlusion *]
    \       opacity=0.5, mode="lighten")

I think above, that backward Occlusion mask should be mixed first with backward SAD mask, same for forward, and then those two mixed together.
(Dont know how MysteryX does it [EDIT: FrameRateConverter], I havnt looked)