Krampus moves fairly fast and deals 50 damage per hit. He behaves similar to a Gobbler or MacTusk when approached. He will break Chests to steal items and will pick up most items lying on the ground in the player's vicinity, including Backpacks. He will keep running around the player until no more items exist on-screen, then disappear into his sack.
Once the player reaches a threshold of naughtiness (a random number between 31 and 50), Krampus will spawn. One Krampus can spawn before day 50, two or three after day 50, and two, three or four after day 100 (see Bugs), all counts being equally likely. After Krampus appears, the naughtiness level is reset to 0.
Each minute of restraint (⅛ of a day) reduces naughtiness by 1, meaning the player can reduce their naughtiness by 8 points by not attacking an innocent creature for one day.
It is worth noting that setting creatures ablaze will not raise the player's naughtiness level. This is because the fire is considered to be the killing factor. The same goes for Tooth Traps, Bee Mines, Gunpowder, and Slurtle Slime, as they are all considered to be environmental damage. This is not to be confused with cooking creatures in a camp fire or fire pit which does increase the naughtiness of the player and can bring forth a Krampus visit.
Without adequate preparation, Krampus, especially when more than one spawns at the same time, could wreak havoc in players' bases. Players are advised to pay attention to the signs of naughtiness, and only summon Krampus when preparations are complete, away from important items and the player base. Krampus can be summoned by killing a number of passive creatures in quick succession. Rabbits can be collected with Traps then "murdered" in the inventory, Birds can be summoned using a Feather Hat, then either captured and murdered by Bird Traps or directly killed using a Boomerang. In Reign of Giants DLC, killing Glommer will immediately summon Krampi. In Shipwrecked DLC, killing seal form of Sealnado will also summon Krampi immediately. Shark Fin Soup adds 10 points of naughtiness, which can also be used to summon Krampi. Killing Doydoys adds progressively more naughtiness as there are fewer Doydoys in the world. Killing the last two Doydoys will guarantee a Krampus spawn each, however, this is not recommended as this makes it impossible to breed more Doydoys later. This can be circumvented by bringing two Doydoys from the group to a volcano, as it's considered a separate world for the purposes of Doydoy numbers.
Krampus' high melee damage and tendency to avoid the player makes him difficult to deal with using melee weapons. However, his low health make the ranged weapons, especially Blow Darts, effective. If melee is the only option, players should wear Armor and use high damage weapons such as a Dark Sword or Ham Bat to avoid significant health loss. He can also be put to sleep or frozen, to make him an easy target. Placing a number of easily obtainable item such as single pieces of Twigs, Cut Grass or Pine Cones will keep the Krampi occupied allowing the player to close in to the melee range.
Summoning Krampus at night time will cause sleeping Krampi to spawn, making it easier to kill them using melee weapons.
Below is the number of hits it takes with each weapon to kill a Krampus when playing with characters with a default damage modifier. The Weather Pain is not included due to the random nature of its projectile.
- Summoning Krampus at night will summon sleeping Krampi, including during a Full Moon, which allows him to be easily killed. This can be combined with picking Glommer's Flower, which only spawns during Full Moons. Killing Glommer, which follows its flower, guarantees a Krampus spawn.
- Tooth Traps are not very effective against Krampus, since there is a chance that he will steal the trap instead of activating it.
- Various forms of "Krampus traps" can be created utilizing their behavior of stealing items:
- Placing a Chest with dummy items surrounded by Bee Mines.
- Placing a Chest full of Killer Bees.
- Placing a Chest and attacking him while he is busy stealing the dummy items.
- A Frog's tongue attack will make Krampus drop stolen items (if they do not kill him outright).
- The Krampus Sack does not burn, but all other drops will be turned to ash if Krampus dies from fire damage.
- In Shipwrecked DLC, Krampi can be lured to their death by placing a Coconade on the ground and lighting its fuse. Krampi will attempt to steal the Coconade, which can explode near them or in their inventory after they steal it, instantly killing them.
- Krampus was added in the Naughty and Nice update.
- Before the Six Feet Under update, Krampus's eyes and "mouth" are originally yellow-green with his eyes possess side-way slit pupils. After said update, he was given a new look. He was retextured with complete white eyes and a purple "mouth".
- Despite this, however, Krampus's icon for the World Customization remain unchanged.
- According to the code in kramped.lua, plural of Krampus is "Krampi". This name is used when calculating how many should spawn at the same time.
- Krampus is a beast-like creature from the folklore of Alpine countries, thought to punish bad children during the Yule season by whipping them into submission. Krampus is said to capture particularly naughty children in his sack and carry them to his lair. Krampus' contrast to Saint Nicholas is reinforced by the Charcoal he carries. Traditionally, naughty children are punished with coal in their stockings.
- Krampus might also have some references to the Scandinavian Yule goat, an old pagan tradition originating from Norse mythology. Note that Krampus' horns resemble ones of an ornamental straw goat and in Finnish tradition, young men used to wear goat heads made out of straw (notice the Krampus' figure) in the Yule season, while going house to house demanding food and alcohol. The Finnish version of Santa Claus still has the name of the Yule Goat.
- Krampus also appears similar to reports of the Jersey Devil, a winged red horse with horns. However, Krampus has no wings and has a much thicker tail than a horse, more like a kangaroo or lizard. He also fights similar to a kangaroo's "kickboxing", standing on its tail and kicking with both feet.
- Glommer is the only mob to increase naughtiness by 50 points when killed by the player, the exact amount needed to spawn Krampus.
- In the Shipwrecked DLC, Krampus appears to have four arms, two carrying his sack and two sticking out from his sides.
- In Base game and Reign of Giants DLC, there is a bug in the code that prevents the 100 days scale up from happening, so in those the number of Krampi spawned will not exceed 3. This bug is fixed in Shipwrecked DLC, correctly spawning up to 4 Krampi after day 100. The fix will be effective in any Shipwrecked or Shipwrecked compatible worlds.
- Hitting Krampus as he jumps into his sack will cause him to reappear and become invincible. Krampus will not be able to move and cannot be killed (he can still be frozen and put to sleep like normal).
- Sometimes two Krampus can spawn before day 50, this only occurs before day 5.
- In Shipwrecked (DLC) Krampus won't be spawn if the player happens to be on sea, even though the naughtiness points are maxed. But he will spawn when the Player kills a mob that gives naughtiness points.[verification needed]