Jalapeno Poppers - When a Guardian's shields pop, they emit an AOE damage (using their subclass's element for the burn) that applies to other Guardians as well as the enemy. Don't bunch up kids.

Black Rain - ADS starts a "Marked by Void" screen effect (a la the Raid). Won't actually kill you, just will kill your peripheral vision and soon your entire FOV. Stop ADS and you will "see clearly now the rain is gone".

Hot Potato - Any time a Guardian jumps, the area in which they jumped in will have a slight AOE damage that applies to everyone. Sort of like what happens when Fanatics die.

Reflection - Rounds which are not one-shot kills will bounce like a specular reflection. Although I think skip rounds already do this, albeit on hard surfaces, not enemies themselves.

-Supers Disabled

Excellent.

-Heavy Weapons disabled

Excellent.

-Special Weapons disabled

Maybe excellent, although it could have some of the same issues as disabling primaries...

-Turbo: game runs at 2X speed

Sure, if the framerate is also doubled ;)

-Consumable use disabled

Maybe excellent, though maybe also annoying when relevant.

-Only critical hits do damage (minus minotaurs)

And sharks. D:

-Half ammo capacity

Excellent.

-All enemies shielded

Heh, it already sometimes feels like that's a thing.

-Hardcore: all enemies 1 hit kill you

Lol.

-Reversey : weapons with lower attack do more damage

Khvostov time :D

-Random Loadout: you've temporarily given three weapons which you cannot change

Lol.

-Mirror : story mission is played in reverse

In addition to taking a lot of work to implement, that doesn't sound interesting. "Yay we killed the boss, let's go punch out a bunch of level 2 dregs then run to a random location."

A modifier that restricts the level to just the intense spot(s) might be cool, though.

-Butthead : No HUD

I think I'd only like that for screenshots, and turning the HUD off really should be a feature anyway.

-Extravision : FOV is set to 180 degrees.

180 can't work with perspective projection; if you're going to go that far, you might as well take the next step and crank it up to 360.

-Tunnelvision : FOV is set to 35 degrees

-Time limit : mission has a time limit

Excellent.

-Bullet eater : only get ammo when you are hit

To be turned on alongside the 1-hit kill modifier.

-Unlimited glide / double jumps

I'm trying to imagine where that would actually work in the existing material as a half-sensible modifier. Would make a good occasional laugh.

-Random enemies : Hive on Venus, Fallen on Mars, etc

Shark -> Phogoth

-Supers Disabled
-Heavy Weapons disabled
-Special Weapons disabled
-Turbo: game runs at 2X speed
-Consumable use disabled
-Only critical hits do damage (minus minotaurs)
-Half ammo capacity
-All enemies shielded
-Hardcore: all enemies 1 hit kill you
-Reversey : weapons with lower attack do more damage
-Random Loadout: you've temporarily given three weapons which you cannot change
-Mirror : story mission is played in reverse
-Butthead : No HUD
-Extravision : FOV is set to 180 degrees.
-Tunnelvision : FOV is set to 35 degrees
-Time limit : mission has a time limit
-Bullet eater : only get ammo when you are hit
-Unlimited glide / double jumps
-Random enemies : Hive on Venus, Fallen on Mars, etc