I put the cc slant effect on an image just to slant (move) the clouds, but it ends up sliding the whole image. The same goes for many other images even after adding a mask. The whole image keeps sliding with the slant.
Not exactly sure what the problem is. However, try making a adjustment layer above your footage. Apply your mask to it. Then add a transform effect. It has a skew and skew axis that can be keyframed