Ores[]
Normal ores can't be found above y=30 in biomes other than the Desert Wasteland, salt ore is the exception to this.
Coal, Iron, Copper and Lead are twice as likely to spawn in biomes where they are restricted to y=30 and below.
It's generally recommended to spend time looting structures, or find a library in the badlands to unlock quarries instead of mining normally.
Gas[]
Gas is a naturally occuring hazard that appears at y 30.
It appears as a translucent yellow mist that completely covers the screen when below it.
It damages any non-undead, non-parasite entity not wearing a gas mask beneath it's surface, dealing 1 damage every 35 ticks.
Unburied[]
Unburied spawn around the player in darkness. They attempt to spawn every 60 ticks on stone or terracotta blocks and are more likely to spawn the lower the player's y level.
Cave Ins[]
Breaking blocks may cause other nearby blocks to fall if they aren't properly supported, you can stabilize the area by supporting it with any kind of vanilla log, vanilla fence, or quartz (with the exception being quartz slabs and stairs, double quartz slabs do not support the area). Placing a support block will prevent the surrounding 17x3x17 area's blocks from collapsing. The support block must be touching a block above and below to support the area.