Summon A No Damage Slime?
Solution 1:
Using the command
/summon Slime ~ ~ ~ {CustomName:"BeingSlow",NoGravity:1,Invulnerable:1,Size:3,Silent:1,ActiveEffects:[{Id:18,Amplifier:10,Duration:999999}]}
Will summon a slime with a weakness over 100% meaning every time it will hit you there will be no damage.