The Day It Changed (TDIC) is a mod that is currently being worked on by one person. Me!.

This mod aims to bring some sort of realism of gameplay making basic resources a pain to gather.
The thing that's different about this is that there will be increased zombie spawns during the night, kind of like a zombie apocalypse.

Well then, the questions your asking!

How does this change Minecraft?

Firstly, you spawn in a dimension very similar to the overworld but with fake blocks, these fake blocks are very similar if not basically vanilla blocks. These blocks are stronger and give basic resources such as:
-Grass and Dirt dropping Dirt Piles.
-Stone dropping Stone Dust.
-Logs dropping bark.

Just makes the resources into smaller parts, using smaller parts to craft stronger parts.

How does this make Minecraft harder?

Well during the day its pretty simple, gather resources, explore, build, do whatever you can!

But when it turns night, you better hope you have a base, multiple zombies will spawn and attempt to kill you. Making night very dangerous.

Blocks don't drop their own block, they drop smaller versions. For example, dirt dropping Dirt Piles, Stone dropping Stone Dust..

How do I start?

Spawning in will be overwhelming, but first you should find gravel and try get flint, then you should destroy leaves. Then destroy grass plants to get plant fibre, once you do that combine your flint, fibre and stick to make your very first flint tool!

This mod will test your skill at surviving by giving extra resources to work with, these resources are similar to real life and default crafting isn't the same.

The zombies are taking over...
Find the cure...
End it all...