A broken and frozen machine.

Freezing is an environmental hazard caused by reaching the maximum altitude and is used as height border to prevent lag and glitches. It is also used in Valfross levels 35 and 41. Freezing only affects burnable parts, such as wooden structural blocks. Burning a frozen part will thaw it.

Freezing does not affect creatures.
Freezing example

Creatures and non-burnable parts are not affected by freezing.