Make the night darker

I’d like the night to become incredibly dark again; also, sleeping in uncomfortable surroundings should result in nightmares. Sleeping outdoors without torches should trigger attacks by Phantoms.

And if you sleep under a roof but in an open area—unprotected from the outside world—then zombies, skeletons, and spiders should attack.

This way, players would have to craft Night Vision potions to roam around at night.

Also, make the visibility of specific stars depend on the surrounding light levels. In other words, if it’s bright, only the brightest stars are visible, but if you remove all light sources, dimmer stars become visible too—allowing players to enjoy the night sky.

Additionally, add a sanity meter that decreases when you hear cave sounds or find yourself in pitch darkness. If sanity drops to zero, Phantoms should appear—encouraging players to use beds—and scary sounds should play.

Sanity could be restored by eating Suspicious Stew or by waiting for morning.

I realize that adding this to the standard game might not be the best idea, but a separate mode featuring these mechanics could be created. For instance, "Casual" mode would remain as the game is now, while "Survival" (or "Real Survival") mode would include these more challenging features.

You could also add a flashlight—crafted, perhaps, from Glowstone, Redstone, and a Spyglass. It would generate light blocks in the direction the player is looking, reaching a distance of 16 blocks.