Warden

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The warden is a hostile mob summoned by sculk shriekers. They are completely blind, and thus rely on vibrations and their sense of smell to identify the player and other mobs. They are extremely powerful, having the highest health and dealing the most damage of any mob in the game, including bosses.

Spawning
Wardens do not use traditional mob spawning mechanics. If a sculk shrieker is activated too many times, a warden will emerge from the ground. The warden will despawn by digging in the ground if it is not agitated and has not detected a vibration in one minute.

Behavior
Wardens are blind and wander randomly. If a vibration is made nearby, it will alert the warden and it will move toward the location where the vibration originated. It can also smell the area around it, allowing it to zero in on an entity's location. The more vibrations a mob or player makes, the more agitated it grows.

The heart on its chest creates a low throbbing heartbeat sound, in tandem with the darkness effect. The animation and sound will speed up gradually as the warden becomes more agitated. Warden will prefer to track down mobs that it is more suspicious of, rather than the closest one.

Once a warden reaches a high enough level of agitation, it will roar and begin directly pursuing the target. The warden will pathfind to the target normally, regardless of vibrations made. If a mob or player collides with a warden, it will immediately enter its angry state.

After sixty seconds of being "calm" and not detecting any vibrations, the warden will burrow back into the ground and despawn.

The warden is classified as an undead mob, which means it takes extra damage from the Smite enchantment, gets healed by the Instant Damage status effect, is damaged by the Healing status effect, and is immune to Poison and Regeneration.

The warden deals an exceptional amount of damage, enough to kill a player wearing full Netherite armor on Hard difficulty.

Trivia

 * Killing a warden doesn't count for the Monster Hunter advancement, nor is it needed to receive the Monsters Hunted advancement.
 * Previous names considered for the warden were the "stalker" and the "hollowed".
 * The stalker iteration was tall, asymmetrical and had a glowing core. It occurred in totems throughout the Deep Dark. The stalker would stand completely still to trick players into taking its core and aggravating it, and could transform into a one block high form to prevent players from digging away. That iteration, specifically its appearance and transformation mechanic, felt clunky and was more goofy than scary, which is why it was scrapped.
 * The hollowed was designed with the intent of inciting trypophobia and had white flesh with holes in it. That iteration was deemed too gory by the developers and had to be toned down.
 * In the sixth episode of “The Secrets of Minecraft” it was jokingly revealed that the warden’s personal name is William, similar to how the ender dragon, the wither, and player characters all have personal joke names. The word was also jokingly broken down into the words: war and den.
 * Kingbdogz stated in a tweet that the souls in the warden’s chest is incredibly important to its lore.
 * Kingbdogz also stated that the warden is inspired by the "monster" heard at the end of "11".

Concept artwork
Some concept art in this gallery was originally made for the Caves & Cliffs update.