Laputan

Fork of Lilliputian by cadaverous_queen (MIT license), a mod that allows random size variation for mobs.

• Changes size distribution to gaussian instead of uniform - this allows extreme variations in size to be more rare and rewarding to come across.
• Scales max health, movement speed, attack damage, knockback resistance, follow range and flying speed to size by configurable amounts.
• Allows additional random variation in these 6 stats by configurable percentage amounts.
• Accurate hitboxes for all mods and sizes.
• No visual "pop-in" effect for mob resizings.
• Highly optimized for performance and bug-free.

Unlike Lilliputian, the config allows you to configure the "sigma" value for each mod (instead of the range) which determines how much size variation the mob undergoes (defaults to 0.0 which is no variation, I recommend 24.0).

Works with all modded entities I tested except Ice & Fire's sea serpent, Fossils & Archeology's dinosaurs (mostly), and Frikinzi's Fauna. It is recommended to blacklist these.

See also Lecovian.