Well, repaired at last.
First thing I noted was the miscoloring of the background graphics/not visualizing the second background graphics layer, and an error in horizontal scrolling.
As I read, probably faulty custom in charge of these sections is 007781.
So changing it for a working one fixes this problem.
But I had a problem left to solve. Bad sprites drawing everywhere.
This error made me feel that the culprit was another custom, and indeed...
These 2 mother******* 2x 007786, completely broken. Replaced both and magic appears...
So in total, the graphic board had 3 broken Konami customs.
P.D.: don't throw away your The Final Round GX870 games, they are excellent donors for Konami Twin 16, xD.