For this, I did a one-piece open mold. The trygon tail didn't have a sculpted underside anyway, so there was no need for a two-parter.
Armature wire, bent to roughly conform to the curve of the mold.
Bottom layer of greenstuff, with the armature bedded into it.
Top layer of greenstuff, smoothed and blended with the bottom.
Not bad. Need to let it dry fully before bending to shape, but I can work with that. Beats doing it from scratch.
Roughed-out tail. Whip it, whip it good.
Started blending the hips to the tail. Bad transition, so I'll need to rework a couple of the plates after the current set dry.