Ultra Mode is a datapack that makes the game much harder and take much longer. You will most likely die multiple times in the early game alone.



Mobs
All mobs, hostile or not, have strength III and speed II. Just a simple zombie can two-shot you without any armor. Creepers are now heat-seeking missiles. Night time without shelter is nearly unsurvivable.

Darkness
When you step into a low light level, you get blindness, limiting vision and disabling sprinting. Hold a torch in your main/offhand or be near light to be able to see again.

No more punching trees
You read that right, you now need a piece of flint or a tool to be able to chop trees. Even when you do break a log, you get nothing but a single stick.

Blocks take long to break
Blocks now have multiple breaking "states" as shown in the images above. Better tools break blocks faster.

Crafting/Survival Guide Up to Iron Age

Breaking grass will give you leaves and plant fibers
Gravel will sometimes give you flint, but will never give you the gravel back
Breaking a log will give you a bark (which is good fuel) and a stick
Two sticks and two leaves will get you an unlit campfire
Four leaves will get you a fire charge

One stick, one plant fibers, and one flint will get you a flint axe
One stick one plant fibers, and two flint will get you a flint pickaxe

Stone will get you 4 pebbles

Four pebbles makes a stone block
Flint axe and pickaxe recipes with pebbles instead of flint will get you stone tools
One stick and one pebble without plant fibers will get you a stone shovel
One stick and one stone block will get you a stone sword

Clay will drop a random of 0-2 clay balls
Cook clay balls on a campfire to get bricks

Four bricks will get you a brick slab
Two brick slabs will make a brick block
Three brick blocks and one clay block will get you a furnace

If it is getting dark, find a cave or dig into the ground to cover from mobs, as they will kill you within seconds
If you feel like you could survive, hold a torch in your main hand or offhand to be able to see while moving around

Find iron in a cave, I recommend not mining into the ground yet as this will take a long amount of time with how long it takes to mine stone

Cooking iron in a furnace will only get you one iron nugget
Four iron nuggets makes an iron ingot
Two sticks and one iron nugget makes two planks
One plank and three iron ingots makes a crafting table
A furnace, two iron ingots, and a stone block makes a blast furnace

A blast furnace smelts ore into full ingots

With iron tools, you can now mine and chop trees more efficiently, as you get full blocks instead of chunks
Two birch logs makes four sticks
Two planks makes a door

Now is recommended to build a house out of planks with a door, or if you don't want risk of it blowing up by creepers, you can continue living in a cave

When you find diamonds, throw them in lava to heat them up, heated diamonds replace normal diamonds when crafting tools and armor, but not diamond blocks

From here, Minecraft is not changed in any way, besides the tougher mobs and slower mining speeds

Info

Resource pack is optional but makes it a lot easier to understand and looks better
All code is by me
Inspired highly by Better Than Wolves (go check it out it's a super fun mod)
Only works for 1.20.4
Current latest version is v1.17
Comment suggestions and bugs and I will always fix bugs and maybe add suggestions
Change log and other useful info: Google Docs