Here’s some:
Miniboss Rush
Increases the number of badass enemies, and a chance that a badass enemy may spawn as a Super Badass.
Armchair General
Increases Action Skill Damage and pet/clone/IB health, decreases gun damage. Increased skill cooldown.
Veteran Spam
Enemies are more likely to throw grenades. Like, a lot. They all maxed their Grenade SDUs.
Friendly Fire
Or, ‘How to lose friends and alienate people’.
Tink Tonk
Loot Tinks are more likely to spawn.
A Spoonful of Sugar
Killing a Badass enemy triggers 15% Lifesteal for a few seconds.
Ultimate Returns
Enemies constantly regenerate health, except bosses.
Opposite Day Mode
Enemy resistances and weaknesses are switched for certain enemies (the ones with upside-down hats).