Affixes: Make your own!

[Unholyground]

Blood Pact. All mobs that are currently aggro'd share a health pool.

That seems like it could potentially be abused quite easily in favor of the group, as a counter measure you would need to add HP to the pool also based on the number of enemies so it is also more of a challenge, maybe like 5% increased hp pool per enemy. I like it a lot though, it would keep certain mobs relevant through fights which means for casters you would have to interrupt or cc them if they are in a group , this has a lot of potential.

[TyrianFC]

Zombie Strippers: Slain enemies are re-animated as angry naked zombie whores.

Ants in your Pants: Any party member who fails to jump at least once every 5 seconds immediately dies.

[pyrostorm9001]

Void Fusion - killing 2 of the same type of mob within a 5 yard radius causes them to fuse together into Larger version of the original mob with a similar in look to the effect from personal hologram toy. Basic attacks can spawn void tentacles that do additional melee damage.

[yango]

Friendly Fire; Every player and npc is attackable and healable

Survivor/Foreverincombat: enemys cant be killed, but if they reach 1 hp they will attack for just small dmg and will have a 60-90% slow if attacked and will run away in fear after a boss kill

Lucky/Fuzzycombat: your movement & skilluse (just the mainskills, so just 3-5 skills) is messed up till the next bossfight (ie: if u click 1 u will use 2 and if u go left, u go back etc but all random

[OrcinusDrake]

So many "double tap" like mechanics, if any of these got added my guess would be one of those.

Skater boy - Running now has inertia. You can slide a short distance after stopping to cast.
Rout - When a player is hit by a cc effect, touching them will spread the effect to other players.
Safety dance - The entire is split into "right side of the path" and "left side of the path" such that you can easily run from one to the other. Every 5 seconds one side explodes.
Battle line - The closer the party is to a straight line (their positions relative to one another) they gain a versatility bonus. (Reduced when not)
Beachhead - The player closest to the centre of the end boss' hitbox gains a versatility bonus. (Reduced from others)
Flanking manoeuvres - Adds spawn intermittently from the start of the dungeon and patrol forward.
Behind enemy lines - No consumables (at all) can be used in the dungeon.
Sentry - Each pack has an add like the ones in stonecore.
Duel wielding - All mobs and bosses now duel wield, doing less damage per attack but more damage overall with more dangerous melee syncing.
Heavy handed - All mobs and bosses swing more slowly for more damage (slightly less dtps) but now also strike the closest party member to the tank (reduced by both their damage reductions including armour). This effect has infinite range.
Claustrophobia - The walls of the dungeon, rather than stopping you running through them, will kill you instead. Don't run off or get knocked back.
Ruins - A whole bunch of bottomless pits and crevices litter the instance. Many you need to jump over rather than just skirt around.
Chaos - At 10% health, bosses gain a damage bonus versus tank specialisations.
Rotting mana - Healing taken reduced by overhealing taken in the past 60 seconds.
Bounce Baby - The player who pulls a mob takes increased damage from them.
Infiltration - Mobs and bosses are initially neutral, but become hostile after your first pull. This effect is reset on a total party wipe and you have a versatility reduction to compensate.
Blitzkrieg - You gain a stacking versatility increase per attack dealt up to a maximum of 20 stacks. Dropping combat for over 2 seconds drops the buff. Reduced versatility to compensate.
Creeps - Packs of small adds slowly spawn and patrol to the entrance of the instance.
Broken cover - Mobs have their abilities, names and models shuffled within each pack, but you now have a "beast lore"-like ability trying you their ability names, attack values, armour and similar "flavour" information.
Long reach - Enemy melee range extended. All mobs and bosses do more damage to and take less damage from opponents that are further away. Stand inside hitbox for a damage bonus against that enemy.
Sidearms - Mobs have 100% more health, but when below 50% (when you'd usually have killed them) their weapon breaks and they'll lose all abilities and just melee you for reduced damage.
Upgrade complete - Bosses have buffed stats when you kill their preceding bosses, but after every kill you gain an item that will upgrade one of your gear pieces by 10ilvls (but not your weapon). This only effects you while inside that instance ID.

[willtron]

Violent Death - All trash explode for X damage upon death. Players explode dealing Y>X damage.
Ground Pound - Area of Effect abilites from bosses are now 200% larger.
Copycat - Trash mobs will mimic one of your offensive abilites at random, at the start of combat.
Denied - Trash and bosses can interrupt casting.
Friendly Fire - AoE abilites also hit party members.
Smelling Salts - Crowd Control abilities last for a maximum for 10 seconds.
Fel Powered - All trash and bosses are infused with fel, all attacks deal fel damage, with a % as a DoT, attacks will increase the duration and damage of the DoT. At 25% health, they explode in a fel fury, sending out a destructive pulse of fel magic reducing all players health to 10% and empowering the enemy with 50% increased crit and haste, but 10% increase damage taken.
Wounded - After every boss encounter you deal X % less damage and have Y% less health.

[krunksmash]

5 o'clock everywhere: all players are ' completely smash ' for the duration of the dungeon.

Slip'n and Slide'n: players slip around as if on ice.

That's not right!?: Bosses use spells other than their own. (Example: a boss would use cookies food throw spell )

[Deleted]

Territorial: Monsters do not move. If you move more than 10 yards away from them a random mob will grip you back and deal 50% of your health in damage.

Personal Space: Whenever you stand within 5 yards of another group member, you recieve ticking damage which increases for every second you remain close.

Holding Hands: At the start of the dungeon 4 members of your party gets paired up with another random group member. If you move more than 10 yards away from your buddy, you are stunned. If your buddy doesn't walk up to you and click on your character within 3 seconds, you both die. In addition, all damage taken is duplicated onto your buddy. If one of you dies from another source, the link remains intact, and you must remain near your buddy's corpse to survive.

Everyone, get in here!: Whenever you kill a boss, all trash mobs respawn.

Duplicate: When you kill a mob, two lesser versions of that mob will spawn. Bosses occasionally spawn mirror images of themselves.

Seeing Red: Your area-of-effect attacks will also damage nearby allies.

Obstacle Course: Traps are hidden through-out the instance. Watch your step!

Expert Timing: All enemies of a pack must die within 10 seconds after you've killed the first one or they'll all respawn and be restored to full health.

[Smank]

Cucked: When the boss is at 1% health, Thrall will run in and kill-steal.

[Wramp]

Undeterred Onslaught - in mob packs of 5 or more, any mob can gain this buff and will randomly choose one player in the group to focus. the mob gains 300% Armor, HP, Movement Speed and Damage, he cannot be taunted or broken from his gaze in any way, can be slowed- lasts 10 secs. this buff can occur on more than one mob depending on pack size, up to 3 mobs at once.
Necrophobic - when mobs reach 5% HP, they can gain this buff and will instantly sprint at 400% movement speed toward any other mob or pack close to them, screaming for help as they run - if they reach another mob before dying, they inspire the mob/pack with 10% HP gain for 20 secs in defense of their dying brother
Unadulterated Insanity - if pulls your group makes in the dungeon consist of 8 or more elites at one time, and you live through the entire fight, you gain this buff and have 20% increased HP and Attack Speed for the entire run or until you die

[AwkwardSquirtle]

Deathrattle: All enemies in the dungeon activate a random effect when killed: AoE Damage, applies a DoT to all group members, buffs allies for a short time, silence a damage dealer, removes all tank threat, etc.
Battlecry: All enemies in the dungeon activate a random effect the first time any threat is generated on them.
Inspire: When a boss successfully uses any ability, activate a random effect.

[draconicman]

"A Day in the Life" - Each player is randomly placed in control of one of their party members when the timer starts and the effect persists for the duration of the dungeon. The player adopts their abilities, bar setup, keybinds, and any abilities on their equipment. The adopted bars, keybinds, and equipment cannot be changed. Professions are unchanged but engineering enhancements on the party member's equipment can be used regardless. Inventory is unchanged but class restrictions on items can become a problem. Addons and macros are not changed either and managing them is part of the challenge of this affix.

[Deleted]

I really dislike modifiers that add concrete things (such as volcanic) as opposed to letting the dungeon do what it's already doing but more/different. Having too many modifiers like volcanic will just make every dungeon start feeling the same. This was the main problem of champs in Diablo 3 in my opinion. It didn't matter where you went and what mobs you fought because all the challenging battles (vs champs) were identical because of the modifiers.

My small contribution:

Disciplined - Any mobs aggroed will call out for assistance and pull every mob pack in the general area (specific size of what constitutes an area would have to be tuned, could depend on dungeon too as in the general area being whatever room you are in or such).

[Deleted]

Get over here, you idiot!: Headless Horseman loses his head every X amount of time, if not killed in X amount of time, random player loses his head and dies (This would only be active on Hallow's End)

Second Life: Every enemy respawn once before dying for good

Punt It : After every X amount of time, Marmot spawns nearby players. Punt it within 5 seconds to gain 50% Haste buff for X amount of time

Hot Footed: Standing still for more than 3 seconds make you take 5% of your current HP as Fire Damage every second

Lowly Gnome: Everyone is turned into Milhouse Manastorm and gets called lowly every 4 minutes, reducing your damage done by 4%. This effect stacks.

Choo Choo: Spawn 5 Toy Train Sets every 5 minutes, making you lose your mind and deal 5% less damage. This effect stacks

Iron Juggernaut: Shuffle a bomb into random players inventory, exploding for 10% of holders maximum life, if not thrown to new player within 10 seconds.


Some of my ideas I thought would be mostly fun, maybe not too challenging

[MeAjur]

Hot Potato: Every 10 sec, fire spawns under each players feat and deals moderate dmg. This fire is permanent.

No! You can take my feet, but leave my feats alone!

[Deleted]

Battle-Hardened - Mobs are now immune to all forms of CC in combat, including slows and snares.

[Deleted]

"Leeching" - Mobs have 25-100% lifesteal (depending on a CM level)
"Slowing" - After killing a mob, entire group movement is slowed by 2%, stacks 35 times.
"Rush" - mobs have 50% less hp, but bosses have 250% more hp, and 50% increased damage.
"Gladiatoral" - mobs have same diminishing on CC as players in PvP do (8-4-1 for poly, etc)
"Undying" - You must kill bosses twice in order to pass
"Freezing" - All damage mobs do is frost (can go also for Fiery/Arcane/etc)
"Reflecting" Attacking a mob gives you a debuff that does damage (think sindragosa)
"Deadly" - mobs have increased critical
"Enflamed" - random fires spawn on random locations every X seconds
"Frenzied" - mobs/bosses gain haste/crit/damage stack on each sucessful hit, up to X stacks (can be dispelled by shiv/soothe etc)

these remind me a lot of Ulduar's Hard modes. Nice.

[Indigenously Abled]

Dindu Nuffin' - Mobs explode in Skittles, Fruit-Juice Cocktail, and Robitussin.

[Flurryfang]

No! You can take my feet, but leave my feats alone!

Wups xD Feet!

- - - Updated - - -

Kamikaze: Mobs no longer die of dmg, but when hitting 0% hp, they start a 5 sec countdown which will end in a glorious explosion, doing 100% of the mobs health in dmg in a 15 yard radius.

Safety dance!: The entire instance is split into cubes. Every 3 sec, 1/3 of the cubes are filled with corruption and explodes after 2 sec.

Not The Alarm!" Every boss in the instance is equipped with a stress trigger. Every time the bosses health goes down with 15%, the stress trigger does a sonic boom, dealing moderate amount of dmg to all players, and silencing for 4 sec.

Did Anybody Bring A Coat?: Chill is applied to all players every 3 sec. The player can remove a stack of Chill by moving their character. The dmg of Chill is increased over time.

Shields Up!: All mobs in the dungeon are now equipped with a force shield. This shield deflects all dmg coming from a specfic direction. This shield changes direction every 10 sec. Bosses are equipped with three instead of 1, but only switches every 30 sec.

Black Water?...Its proberly Alright: For every 5% hp lost, mobs will drop an orb within 20 yard. This orb will glow for 5 sec, after which it will heal the mob for 5% of its HP. The orb will disappear if stomped on by a player. Bosses will have this effect for every 2% of HP.

[idunnowatdo]

Diablo affixes. Wall-chains-vortex-firepools. any combo of those 3