Warden

A warden is a hostile mob summoned by sculk shriekers which is blind and thus rely on vibrations and their sense of smell to identify entities. Wardens deal the most melee damage of any naturally-spawned mob in the game.

Spawning
Wardens do not use traditional mob spawning mechanics. When a player activates any sculk shrieker 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. The warning count for sculk shriekers is specific to each player, not each sculk shrieker. This means that the same player can activate three different sculk shriekers just once and a warden spawns on the third activation.

Drops
Wardens drop three experience points on death.

Behavior
Wardens are is immune to knockback, 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. The warden in this state pathfinds to the target regardless of vibrations made. If a mob or player collides with a warden, or attacks it first, the warden immediately enters its pursuing state.

The warden tracks down and attacks all other mobs, excluding other wardens. The warden can also follow vibrations made by non-mob entities such as projectiles or minecarts.

After a minute of being calm and not detecting any vibrations, the warden burrows back into the ground and despawns. The warden is completely invulnerable while emerging or burrowing, including damage from, though it can still be pushed by entities, pistons and liquids.

The warden's attack reaches a 4x4 cube around it, reaching a target up to four block heights or away and disabiling shields for 5 seconds. This attack deals an exceptional amount of damage, enough to instantly kill a player wearing full netherite armor on Hard difficulty. A warden's hitbox can fit inside a corridor 1 block wide and 3 blocks tall. This allows them to chase entities pathfinding precisely even in small cave corridors.

The wardens are immune to damage from fire and lava. Water does not slow down a warden and bubble columns have no effect on an aggravated warden.

Advancements
There are no advancements associated with the warden. The warden is intended to be a natural disaster that is almost impossible to kill and best avoided. Therefore, killing a warden doesn't count for the Monster Hunter advancement, nor is it needed to receive the Monsters Hunted advancement.

Entity data
Wardens have entity data associated with them that contains various properties.

Trivia

 * Some previous names considered for the warden were the stalker and the hollowed.
 * The stalker iteration was tall, asymmetrical and it 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, so 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 the 11 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 supposed to be blind, spectating it reveals that it still has normal vision.