Is there a way to pause mob for casting a spell with especial animation or another action. ?

I want to make mob act like a boss, doing different actions, for example:
When mob is in passive stage (not targetting player or someone) it may kill a passive mob, then sit down near to it and start eating his flesh, restoring HP.
What procedures do i have to use to make my mob stand still, playing especial animation and dont do anything else (not targeting someone, not wandering, just staiyng and play anim without breaking it by movements)
"Pause entity" or something?
Override it's motion to zero each tick?
Any sane way?