Depending on what difficulty you’re running, Normal as 1, Nightmare as 2, Hell as 3 and Inferno as 4; mobs that spawn randomly in the game are given 1, 2, 3 or 4 random affixes. These are randomly selected from the list below and then those abilities are used randomly against you. So if you’re rolling through Normal and see a rare pack, they will have a single affix. If it’s Plagued that means they will drop green poison that will do a decent amount of damage to you. If you’re rolling through Hell, you might see a combination like: Plauged Frozen Vortex which means they drop poison, drop freezing orbs and suck you to them whenever the hell they want. Here is a complete list of these abilities (in alphabetical order):
Arcane Enchanted – Creates an immobile arcane orbs that rotates a ray of arcane. These look like the hand on a clock going around in a circle. The rotating ray does arcane damage.
Avenger (Rare Packs / Champion only) – As you kill members of the pack their survivors grow stronger. Kill them anyways.
Desecrator – These guys create expanding void zones that do physical damage when you stand in them. They are relatively easy to avoid.
Electrified – Shoots several electric pulses that expand outwards and away from their source. These are painful and do lightning damage, but usually go pretty slow.
Extra Health – They have 150% additional health and therefore are much harder to kill.
Fast – These move 40% quicker so they are harder to kite or avoid.
Fire Chains (Rare Packs only) – The packs will be linked together with a chain of fire. If you cross that link you will take considerable damage.
Frozen - Throws out several frozen orbs that expand slowly and then explode. If you’re caught in their explosion you’re frozen in place for awhile. This is similar to Jailer except Jailer doesn’t require you to get caught in the explosion of an orb; they just decide when you’re going to get trapped without asking you first.
Health Link (Rare Packs only) – The health of the pack is shared, so if you start doing damage to one of them all three will share 1/3 of the damage.
Illusionist – Creates Illusions of themselves. This is more annoying than anything else.
Invulnerable Minions (Elite champions only) – The champion will have a group of minions who are invulnerable throughout the entire battle.
Jailer – Create a jail around you, preventing you from moving. You can still cast, heal yourself, etc.
Knockback – When they hit you with a melee ability you are “knocked back”.
Molten – Leaves a trail of fire/lava behind them. If you step in it you take damage. The lava trails do a considerable amount of damage. Their body will explode after they die, get away from them quickly.
Mortar / Grenadier – Launches fireballs at you that explode when they hit the ground. These come in packs of 3 so you have to keep moving. They do a considerable amount of damage.
Nightmarish – When they hit you with a melee ability (and possibly other types) you are feared for several seconds.
Plagued – Drops areas of poison that do damage when you step in them. These are generally easy to avoid if you’re ranged but difficult if you are melee.
Reflects Damage – Frequently reflects damage back at you, this is extremely annoying and lethal if you’re not paying attention.
Shielding – Creates a shield around themselves, making them immune to all damage. They will continue to attack throughout.
Teleporter – These will periodically teleport wherever they like, if you’re a Demon Hunter this is usually next to you where they will proceed to hit you without your permission.
Waller – Creates walls, often trapping you in and forcing you to approach them in order to escape. Sometimes these are just straight walls that get in your way when you’re kiting.
Vampiric – Absorbs life from you and gains it back for them. This can be a big hassle if your follower keeps taking their bate.
Vortex – Draws you towards them so that they can relentlessly beat on you. This is terrible when combined with Jailer (for ranged) and even worse when combined with plagued and other abilities that you will be pulled into.
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