I would like it to be possible through a creature “power” to transform one creature into another.

Ideally, if a certain spell is cast, it would be possible to execute a piece of the map script.
In this “piece” one could set different animation seti (modifying the part under [sprites] and the part [attributes] and the others, so as to change the creature.
By timer of the script, it could then restore the original configuration.