Demon

Demons are one of the fiercest foes you will ever encounter in the Nether. They guard the Fortresses from trespassers. Beware of their Demonic wrath.

Spawning
Demons replace Skeletons inside of Nether Fortresses (you can learn more about the spawning system in "More Mobs" here). You can learn more about how Skeletons spawn here.

You can also summon a Demon using this command: /function imm:summon/imm/demon. You can obtain a Demon Spawn Frame with this command: /function imm:spawn_frame/imm/demon. Make sure to replace the 'imm' portion with whatever version you're playing on if your version is older than Snapshot 3C (example: Snapshot 2A = imm2a).

General
Demons will pursue players, Villagers, Wandering Traders, Iron Golems and baby Turtles on sight from 40 blocks away, as opposed to 16 blocks in most other hostile mobs. They will attempt to avoid obstacles, including sheer cliffs, water and lava, and will try to find the shortest path towards their target. If the Demon is attacked by another mob it will attack it in return.

The Demon is technically an undead mob, but will not drown. However, it will stomp Turtle Eggs and sink in water.

Exploding
It is possible to give Demons a Golden Apple if they have the Weakness potion effect. Repeating the same process as with curing Zombie Villagers will lead to the Demon creating a large explosion.

Fighting strategies
Players have to be heavily prepared before fighting a Demon. Potions of Fire Resistance are highly advised. Most importantly the Player must avoid other mobs in the Fortress, or lure the Demon out to a safer area. The key to the fight is being able to heal, patience and doing as much damage as possible per once. Pillaring up is not advised as the Thorns enchantment on the Demon's armor is likely to push the attacker off.

Drops
As with all demonic mobs, the Demon has to be killed by a player to drop: (0.85% chance) Held item (Golden Sword enchanted with Fire Aspect 3 by default))
 * 1 Demonic Essence
 * (Exclusive to the Demon):
 * 5 experience

Data values
Demons possess the same tags as all Zombie Villagers, but they spawn with a set of additional stats. Click here to see the data values common to all Zombie Villagers.
 * Health: 75
 * Tags: iMM, iMMNether, iMM_Demon
 * Silent: 1b
 * CustomName: {"translate":"imm.entity.demon"} (§6Demon in English US)
 * CustomNameVisible: 0
 * DeathLootTable: imm:entities/imm/demonic
 * CanPickupLoot: 1b
 * Attributes:
 * generic.maxHealth: 70
 * generic.knockbackResistance: 0.75
 * generic.attackDamage: 7
 * generic.movementSpeed: 0.25
 * generic.followRange: 30
 * zombie.spawnReinforcements: 0

Advancements
The Demon can be required (as the Zombie Villager) for the following advancements (all of which are form vanilla Minecraft):
 * Adventure
 * Monster Hunter

The Demon is also required to be killed for the following "More Mobs" advancements: There's also a "More Mobs" advancement that is granted for surviving a Demon blast:
 * Monsters Hunted
 * Monster Fighter
 * Mob Fighter
 * Gamers Will Not Be Suppressed!

Metahistory
Demons existed in an old unreleased version of "More Mobs" for the Nether. It functioned pretty much the same as the current version of the mob, except it didn't ever blow up.

Known issues
There are currently no known issues with this mob in the latest release.