During the night you can choose following stackable upgrades:
Upgrade King Attack (max x10)
20
Increases the King's attack damage by 12.5%.
Upgrade King Regen (max x10)
20
Increases the King's health regen by 0.0045% missing health + 0.0045% max health
Upgrade King Spell (max x10)
20
Increases your King's AOE ability damage by 5.5%
Each king starts with the following spells:
Giant Slayer
Attacks deal 12-27% current health Pure damage depending on Upgrade King Attack
Lightning Hammer
Uses mana to unleash bouncing lightning bolts that deal Pure damage.
Tenacity
Gains 1.3% damage reduction for every 1% damage taken this wave.