In this example I'm changing the Mythicmobs mob skin to a ninja_skeleton skin.
Animations
As you can see I also added some Skills to replace the mob animation dynamically.
{play=attack} is used to make the attack animation play, in this case when the entity attacks.
{walk=b_walk} is used to replace the mob walk animation b_walk which is an "angry" walk animation, because the mob has just attacked another entity and has a target.
Animation
customentity{idle=ANIMATION} To change the idle animation
customentity{walk=ANIMATION} To change the walk animation
customentity{attack=ANIMATION} To change the attack animation
customentity{death=ANIMATION} To change the death animation
customentity{play=ANIMATION} To play an animation right now
customentity{stop=ANIMATION} To stop the current animation