With the arrival of the fabled Caves and Cliffs update brings a new mob called the Warden, so here's how to kill it.
How to Beat the Warden in Minecraft
The Warden in Minecraft is a mob that was added to the deep dark cave biome and is dangerous. That said, to kill the Warden, we recommend trying a bow with good enchantments, as you don't want to get into close range combat with this monster. You can also throw snowballs or eggs at it to slow it down if it gets too close so that you can retreat easier. Eventually, you might run out of room to fall back, so we suggest making a high advantage point where you can sit up top off and fire arrows at the Warden until they are gone.
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You can also try making a warden trap by luring it into it by firing arrows at it and running back - if you go this route, we suggest making an escape door inside the hole. Once the Warden is in the hole we recommend filling it up with water and then closing it up so that the mob drowns.
However, you might not be able to kill the Warden as the developers intend it to be something players should avoid rather than fight. So due to this, you can still use that hole idea but for trapping rather than killing, but more often than not, you will need to hide from the Warden. To do this, sneak and avoid making any noise, as the Warden is attracted to it and can find you fast if you are loud. The Warden is also blind and can only find you via sound, so if you are quiet, you should be able to avoid him with no problem when he gets added to the game.