Hi
Here 2 animations made with last Krita 5 pre-alpha and use of animation curves on transform mask.
Final result is not really like what I have in my mind, especially for the second one, but goal was more to test functionalities.
It was hard to finish due to bugs, I had to make choice about final render and composition, it took hours and hours and hours to be able to finish it, but that’s not totally a lost time: I’ve been able to detect and open many bugs. Hope they’ll be fixed before release 
Infinite loop of the rotating sausage through black holes warps
A sausage moving through bi-directional black holes warps
Infinite loop pursuit of the rotating sausage through black holes warps
Buli in pursuit of a sausage that’s moving through directional black holes warps
note:
animation are in FullHD (1920x1080) but discourse doesn’t allow to show them in full format… need to right-click and then ‘Display image’
Grum999