The "programming" behind custom Characters (Monsters) isn't a big problem, but the skins need a lot of time ( ~ 45 skins for a good animation).
You have to declare all the animation - texture - coordinates [start: x/y] & [+x/+y] of the image file and the texture times. (in the .xml file of the Character)
The real programming behind the Characters are the "behaviors" (melee, ranged, spawner, caster...) but I have currently no idea how to make a "behavior" :/
I hope my English is understandable.