Granted, You now cannot do any of the following all of which could potentally lead to conditions where you might suffocate
- Stand under sand or gravel
- Ride a Boat, Minecart or a pig
- Stand near a sapling or a mushroom.
- Kill an Ender Dragon.
- Use a Piston at head height
- Throw an Ender Pearl
- Sleep in a bed
I wish you to enjoy your hacked version of minecraft