Changes:

Changes that make the game harder:

Bee- Very fast, lots of damage (I think I left them neutral though)

Blaze- Machine-gun fire. Bring fire resistance.

Cave Spider-  Pounces from above. Lots of damage.

Chicken- Runs away like a rabbit.

Cow- Also runs away like a rabbit.

Creeper-  Sees you through walls. Also blows you up through walls. Make your walls three blocks thick if you don't want it to be suddenly blow up in a fiery explosion.

Drowned- More health, weakness effect, sometimes carry golden swords.

Elder Guardian- More health, more damage.

Ender Dragon- No longer nests. Constantly charges you. More health. Fire balls insta-kill without blast protection armor.

Enderman- More health, more damage, blindness effect.

Endermite- on the rare occasion you spawn one, it pretty much just insta-kills you.

Evoker- More health, faster, spawns normal things as well as phantoms, ravagers, the occasional zombie army, and very rarely a wither. Also try breeding them with bones! You will get a "nice" surprise. 

Ghast- Triple shot, faster, bigger explosions.

Goat- I haven't really tested it, but they should ram you more often and harder.

Guardian- More health.

Hoglin- Fast, no knockback, more health, I think I added mining fatigue effect.

Husk- No knockback, lots of damage, Curse of the Mummy (actually just bad omen)

Magma Cube- faster, more damage.

Panda- higher chance of aggroing you, lots of damage.

Phantom- Very fast, lots of damage, no longer burn

Pig- Runs away from you

Piglin- Aggro no matter what, poison arrows, lots of damage, occasional netherite sword. Also sometimes carry golden axes.

Piglin Brute- Carries undroppable netherite axe.

Pillager- Very fast fire, faster movement, more health, sometimes carries bow instead of crossbow.

Polar bear- hostile, lots of damage.

Pufferfish- Long lasting poison effect. Guaranteed death without milk.

Ravager- Fast, lots of damage, lots of health.

Sheep- Runs away from you.

Shulker- No more slow levitate. This thing will toss you in the air like a rocket. Practice your MLGs.

Silverfish- poisonous, more health, more damage.

Skeleton- fast, sometimes carry stone sword. More health, no longer burns.

Slime- faster, more health, more damage.

Spider- VERY fast, wither effect.

Stray- Makes you frozen temporarily. Sometimes carry bow, sometimes carry crossbow, sometimes carry stone axe.

Vex- faster, lots of damage. Carries diamond sword.

Villager- Runs from you very fast. They probably figured out you plan to enter them in the slave trade.

Vindicator- Very fast, more health. Carries axe OR sword. Now slaughters villager children as well!

Witch- More health. There wasn't much I could change in the stuff I had access to.

Wither- Don't, just don't...

Wither Skeleton- No more wither effect!... but they do have full netherite gear.

Zoglin- Faster, more damage, no knockback.

Zombie- No knockback, slightly slower (except the babies), poison effect.

Zombie Pigman- DO NOT HIT ONE OF THESE!! They take reinforcement to another level. They simply keep multiplying until you're dead.

Zombie Villager- Same as zombie.

Here are some of the buffs I added to just make the game a little bit easier:

Golden Carrots- Now further overpowered. Can be eaten very quickly, and remove negative effects only. Also more common in chests.

Illagers- All illagers have a chance of dropping a totem when killed.

Snowballs- Now do one half heart of damage!

TNT- Bigger explosion.

TNT Minecart- Bigger, fiery explosion.