Tutorials/Defeating a monster room

Monster rooms are structures that generate underground connected to caves or other generated structures. They contain up to 2 loot chests and a monster spawner that spawns zombies, skeletons, or spiders. The spawner can be farmed for experience and mob drops and the chests can contain useful and valuable items as well, so they are very good to find.
== Item loadout ==
* Torches or other light sources to disable the spawner, as many as possible
* A sword, stone or better, preferably enchanted with Sweeping Edge, Sharpness, if possible (Knockback and fire aspect are optional)
* A full set of iron or better armor, enchanted if possible (although if you are experienced enough, you may not need armor).
* A pickaxe
* Nutritious food like bread or steak
* Plenty of cheap building blocks, such as dirt or cobblestone
* A golden apple (optional)
* A shield (optional)
* Potions (optional)
* A lava bucket (optional)
* A water bucket (Always recommended for mining trips)
== Finding a monster room ==
Monster rooms generate at any altitude provided they are next to a cave, even if "Generate Structures" is turned off. If you stumble along naturally generated cobblestone when mining or exploring underground, that's a good sign you might have found a monster room; however, water and lava mixing also generates cobblestone, so be careful when investigating. Mossy cobblestone generates a lot in the floor, and there are only five naturally occurring sources of mossy cobblestone: monster rooms, jungle temples, pillager outposts, villages, ocean ruins and mossy cobblestone boulders. So, if you're not in a jungle biome or aboveground, you've found a monster room.
Monster rooms also generate next to caves. Turning sound on can be significantly helpful and subtitles still help. If you hear a lot of mobs of the same type in one direction, chances are there's a spawner in a monster room. The spawner has a chance to be a zombie (50% chance), skeleton (25% chance), or spider (25% chance). Unlike most generated structures, monster rooms cannot be located with .
== Defeating the monster room ==
Once you've located your monster room, turn on subtitles or sound to determine what type of monster room it is and how to prepare. 
* If it's a zombie monster room, take care to note what difficulty you are on. If you are on hard difficulty, additional zombies can spawn as you're dealing with the zombies in the spawner, attacking you from behind. Smite will be the most effective sword enchantment here, as well as a shield and good armor.
* If it's a spider monster room, know that spiders can climb walls and are 1 block tall but can't fit in a one wide gap. Spiders are affected by Bane of Arthropods.
* Skeleton monster rooms might be the best type of monster room, but is also the most dangerous type to defeat. Projectile Protection armor will be helpful, and a shield is absolutely essential. Note that skeletons are the same size as zombies but can still shoot through gaps. Like zombies, they are affected by Smite.
If you've found a zombie or spider monster room, immediately block up the entrance with building blocks, and make a 1x1 hole in the monster room's wall. If you can reach the spawner from the hole, place a torch or another light source on or near the spawner as soon as possible, so that fewer mobs will spawn in. Use your sword to fight the zombies and spiders as they come. New groups of 1-4 zombies or spiders will spawn every 10-40 seconds if the light level is insufficient, so when you've defeated all the current mobs in there, quickly break in and scatter torches everywhere to deter mob spawning. Don't look in the chests unless you're absolutely sure no mobs will spawn, as being ambushed while looking at a chest can be deadly. Remember that all monster rooms generate an entrance, so you could be attacked by creepers or skeletons from outside if you haven't prepared well.
The spawner in the center of the room is the key prize. You can destroy it if you like (it gives a modest amount of experience when broken with a pickaxe) but that is strongly discouraged unless you never, ever, ever want to farm the spawner. Once you're done, look in the chests. The loot normally contains a lot of things, but the best prizes are golden apples, horse armor, name tags, enchanted books, and saddles.
If you've discovered a skeleton spawner, follow the advice above except always have your shield at the ready. Skeletons will fire at you from afar, so have a bunch of arrows and know how to shoot as soon as the bow is fully charged. If you have enchantments on the bow, relatively high levels of Power can kill a skeleton in one shot.
== Aftermath ==
Spawners can make very useful experience and mob drop farms.
* Zombie farms can offer tons of , but might also give the occasional , or . Random armor, s or s might drop if the mob spawned with it. 
** If converted to a drowned farm, it gives rotten flesh and s.
* Skeleton farms offer s (for or s) and s, as well as the occasional armor or s, which are sometimes enchanted.
* Spider farms drop s and .
All of these mobs will also drop experience upon death.
Advice on how to make farms of these mobs can be found on the Spawner Traps page.