You can't craft stone or iron tools until you are smart enough. To get smart enough you must throw 16 books, 64 stone, and 8 string on the ground. You will get a notification in chat, and you will be able to craft stone tools. To craft iron tools you need 64 iron ingots, 16 books, and 16 string. This is so you can't get stone or iron tools on your first day.

Whenever you craft iron armor, it will be changed to chainmail armor. And diamond will be changed to enchanted chainmail armor. This is to provide more of a challenge.

doing things like walking, sprinting, jumping, and taking and dealing damage will deplete your thirst bar. Drinking water, milk and any type of potion will help your thirst. Be careful though, if your thirst gets down to five, bad things will start happening.

Limited inventory

One of the first things you'll notice is that your inventory space is halved. you can only use your hotbar and the row above it. It is possible (though unlikely) that when you shift click an item from your hotbar to your inventory, the item will disappear. If that happens, you are allowed to cheat it back in.

Food

After one in-game day, all food in your inventory will get rotten and it will get cleared from your inventory. This is so you have to keep finding and cooking food to survive. Apples, carrots, melon, and beetroot will never get rotten though. Also, eating raw meat will poison you.

Health

This module turns off natural regeneration, so that the only ways to heal are golden apples, health potions (if you can get a hold of them), and mushroom stew which will heal two hearts.

Mobs

Zombies give you hunger when you are near them

Other

Stone and cobblestone will give you slowness when they are in your inventory. Chests are not allowed and will be cleared from your inventory. However you can use droppers, dispensers, and naturally generated chests. Keep in mind though that you have to leave the chests where they are, because if you pick them up, they will be deleted.