The Hail Boss is a boss from the Weather Mobs idea pack. It is summoned when one uses an Enchanted Hail or with a 1% chance when a player takes hail damage. It will not stop hailing while the Hail Boss is alive; if the hail is turned off with a command or mod, the hail boss will despawn instantly. The Hail Boss has a total of 150 health (75 hearts).
The Hail Boss appears to be an immense hailstone. The hailstone has an angry face on it.
In the first stage of the fight, the Hail Boss will fly about 20 blocks above the player and drop Snowballs on them. The Snowballs do two durability damage instead of one to armor, and also do damage.
The second stage of the fight is triggered when the Hail Boss reaches 50 HP (25 hearts). Its face turns into an O of surprise instead of a pout, and it starts summoning Angry Hail into the fight. In addition, huge hail meteors start falling from the sky. These hail meteors will make explosions the size of TNT in the ground and replace all blocks they destroyed with Ice.
Note that the battle is best done in a well-lit arena; this keeps out the normal nighttime mobs.