Body morphing

This implies (gradual) changes to to characters polygon mesh and similar. For sprite based games this is probably harder to make as impressive (vector graphics could help with that, though).

Note that this is generally not for where meshes or sprites get swapped directly to some other variant, but rather where they change dynamically. With polygon meshes this isn't actually that hard to accomplish or even that demanding of the system, but with sprites it requires vector graphics for smooth transitioning (and altering basic pixel art procedurally is quite a bit more roundabout than when dealing with vectors/polygons).