Mob Variations
Causes most naturally-spawned mobs to have randomized stats!
Mobs can have edited Size, Movement Speed, Jump Strength, Attack Damage, and Max Health.
These randomizations will apply to all mobs of any eligible type, including mobs spawned naturally by the world, by spawners or spawn eggs, or with /summon.
To spawn a mob that won't get randomized stats, summon it with the tag "mobstats.ignore".
Stats are randomized between a set of maximum and minimum values. These values are saved in the scoreboard objective "mobstats.range" - to view/alter them, put this objective on the sidebar, and edit the values you see. Any changes will apply to any mobs spawned from that point on, but not already-existing mobs.
To change which mobs can be affected by which stats, you can edit the respective entity_type tags inside the datapack.
Explanation Video Here
Read more on the PlanetMinecraft Page