hard as nails is a mod that aims to make survival in Minecraft worlds more complicated, by adding the concepts of thirst and temperature.
The mod takes care of generating various stations, where the ambient temperature and the thirst of our character will appear. So now, in addition to feeding our character, we must also watch over his body temperature and hydration, either by lighting a fire or by drinking water.
In addition to this, the mod adds various items, such as new armor, environmental thermometers to determine ambient temperature, and a clock or calendar of seasons, among other items. The seasons will change the appearance of the foliage of plants and trees.