It will be a lot of work to add these animations unfortunately, you'd need to:
- Convert the video into PNGs and restore the alpha channel in the background (by itself might already be a ton of work).
- Convert each anim frame to match the in-game format: resize, crop, center ("origin" values in UndertaleModTool) so that the animation is aligned with the original one
- Code the animation to display as variant
I can offer to do step 3) but not 1) and 2) as this is too much work for getting just one of the 30+ animations that would be needed for a nude mod (and for an enemy that we already have, on top of it). We will still need to find an artist to draw all the remaining ones regardless.
Basically if you or someone else replaces the animation in the data.win and it looks good then I can easily merge that in my mod and write code to trigger it as an optional variant, but be prepared, this is several hours of tedious work.