Entity movement

My cousin wanted me to make a gamemode in minecraft, which is basically game "The Hunter: Call of the wild". I've made some 3d models of animals. I wanted to teleport the 3d model to for example pig, and i don't know how to detect if the pig is moving. Could you also help me with not making the 3d model's teleportation so choppy? And, how to leave the pig's hitbox, but replace it's ai with zombie's