Warden

bedrock

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 the most powerful of all the monsters, 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. When a sculk shrieker is activated three times and there isn't another warden within 48 blocks and the light level is lower than 11, a warden emerges from the ground. Up to 20 attempts are made to spawn a warden within a 11×13×11 box centered on the shrieker. Wardens require a a light level of 11 or lower to spawn. The warden despawns by burrowing into the ground if it is not agitated and has not detected a vibration in 1200 ticks (one minute).

The warden is completely invulnerable while emerging or burrowing, including damage from /kill, though it can still be pushed by entities, pistons, and liquids.

Behavior
Wardens are blind and wander randomly. A nearby vibration alerts the warden, which moves 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 souls on its chest creates a low throbbing heartbeat sound, in tandem with the Darkness effect. The animation and sound speeds up gradually as the warden becomes more agitated. Wardens prefer to track down mobs that it finds most suspicious, rather than the closest one.

Once a warden reaches a high enough level of agitation, it roars and pursues the target. In this state, the warden pathfinds to the target normally, regardless of vibrations made. If a mob or player collides with a warden, or attacks it first, the warden immediately enters its angry state.

The warden tracks down and attack all other mobs, excluding other wardens. The warden can also follow vibrations made by non-mob entities such as projectiles or minecarts. After sixty seconds of being "calm" and not detecting any vibrations, the warden burrows back into the ground and despawns.

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, is immune to Poison and Regeneration, and is ignored by the wither. However, unlike some undead mobs, the warden does not burn under direct sunlight.

The warden's attack disables shields, and deals an exceptional amount of damage, enough to instantly kill a player wearing Full netherite armor on Hard difficulty.

Wardens can fit in a 1 block wide and 3 blocks height corridor, due to their hitbox. This allows them to chase entities pathfinding precisely even on small gaps, such as cave corridors.

The warden is meant to be a natural disaster that is almost impossible to kill and best avoided.

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.
 * Brandon Pearce (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" (a music disc).
 * Coincidentally, in the spinoff game, Minecraft: Story Mode, there was a character who was also named the Warden. It is unlikely that the mob was based on the character.
 * Although the warden is intended be blind, when one spectate the warden in spectator mode, it gives out a normal vision.

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