The burning sun
In this modification, the sun becomes unbearably hot and dangerous! When you're under direct sunlight, your character starts to ignite. The only salvation is to hide under any blocks that will provide you with shade and protection from the scorching heat.
Interestingly, this threat completely disappears at night - you can safely move around the world without the risk of spontaneous combustion. This feature adds a new level of strategy to the game, forcing you to carefully plan your daytime movements and seek shelter.