Transition between characters

I am not sure I completely understand what you need - e.g. are they two "profiles" of a character animator puppet that you want to transition between? There is a "cycle layers" behavior which allows you to display a series of frames, but you have draw the in-between frames yourself. Character Animator allows you to move eyes, move arms up and down, etc. It is 2D, not 3D, meaning there is limited support for the character turning (there is some parallex support, but its like for small turns, not full body turns - e.g. eyes, mouth and nose move towards the right when head turns).

If you are looking for tools to morph between the two images you have, cross fade (as TheOrginalGC mentions) is certainly possible. Adobe Premier Pro appears to have a "morph cut" feature that *might* help, but the quick video I just saw made it feel like to smooth out small transitions, not big ones.

So it depends how sophisticated you want to go and the problem you are trying to solved. The artwork is so different in this case I suspect a smooth transition will be hard without drawing the in between frames yourself.

Assuming that adding more frames is not an option, perhaps you can add the fader behavior to the puppet and overlap the timeline for the two?