Help with entitys please :'(

Hi, i'm making a mod that has a boss that emerges from ground, and because you cant add animations i did 3 entitys called ''mob_name''animation1-2-3, so when you right click a summoning block, it will spawn the animation 1, despawn it, spawn animation 2, kill it, spawn animation3 kill it and then spawn the mob, the problem it's that for some reason, I cant despawn the entitys that are called animation, when i use the despawn event/target entity the entity don't despawn! I tried to enable AI and hitbox again, but it still dont work! So please if someone know what i can do, tell me please!