Skulls

Skulls are optional difficulty modifiers which can be activated in Defiant Mode, or the Daily and Weekly Hardcore Challenges. They normally make the game more difficult for the player.

Skull Name	Ingame Description	Effects
Bankrupt	No nuts drop. Make your own way.	No nut pickups drop. No nut-related Augs spawn (Armor Nut, Charged Nuts, Forgotten Memento, Health Nut, Meganut, Nut Replicator, Nutsaving Stringwire, Nutstack, Scrapmetal Scavenger, Skittery Smuggler). Shops and Dispensers no longer appear.
Dearth	Only the first three bosses grant their normal rewards. Choose wisely.	A maximum of 3 boss Powers can be obtained, or the player can take a Nutstack or Aug instead. Regardless of choices made for the first three bosses, no post-boss reward choices will spawn at all from the fourth boss onward. The bonus chest can still spawn, and the boss chest always spawns normally.
Destiny	Only one next-level portal at each level's end. Your fate is written.	Only the first boss portal works. The other two are always broken.
Endless	The journey doesn't end until you do. (WARNING: Not well-tested. May crash at high levels.)	At the end of every level starting with level 8, the player can choose to either continue to another standard level or proceed to the Station levels (choosing the latter will allow the player to win the game by reaching the end of the second Station level). Enemy damage and boss health/damage increase gradually beyond level 8. Damage taken increases based on the Fibonacci sequence (levels 9-16 increase damage taken to 2; the next round of eight levels increases this to 3, then 5, 8, 13, etc.).
Famine	No health items drop. Ration well.	No health pickups drop (applies to enemies, crates, boss chests, and bonus chests). Crates that would contain only health contain nothing. Health Dispensers do not spawn. <Are they replaced with Crimson Dispensers? Seeing more of those...> Vitality Scavenger does not drop. <And if you have it from a pre-run Soul Shop purchase, it won't work?> Augments that increase maximum HP, such as Life Extender, increase current HP as normal. Augments that heal without spawning health pickups, such as Health Nut, Regenerative Plating, and Owlhawk's Reign, work normally.
Final Destination	No items. Fox only.	No items of any kind spawn, ever, with two minor exceptions: after defeating a boss, the player can take the Power AND either a Heart Container or a Potato Battery, and Glory Zones offer health/energy pickups as rewards.
Furor	Enemies act faster. Stacks with Lightning. Can you break their technique?	Enemies act at <150%?> speed. Some enemies are not affected.
High Tide	Zone generation level +4. Use if "Starting at Level 5" sounds fun. You're going to die a lot.	Level difficulty is taken from four levels down the line, basically starting the player at Level 5. This means that levels are longer and filled with more enemies, that higher tiers of enemies spawn at the very start of the game, that all bosses have their harder Level 5+ properties, and so on.
Marathon	All levels are longer. Prepare for the longest journey.	Increases the starting level length for the level generation system. Level 1 becomes notably longer than normal, and each subsequent level keeps building on the longer initial length.
Lightning	The game runs at 150% speed. Be swift as a coursing river.	Everything, including the player character's actions, occurs 50% more quickly.
Purist	No movement upgrades or Core Augs drop. Paddle your own canoe.	Speed and jump Augs (Armorall, Boltdash(?), Contractor Omega, Contractor Plus, Crisis Overdrive(?), Mixmatch Mastery(?), Ninja Sash, Hypersash, Kinetic Converter, Leafmetal Plating, Leafpetal, Plumber Hat) no longer appear. No Core Augs appear. Glory Zones offer regular Augs as rewards.
Rock	Spikes, pits, spike-like things, lasers, and lava (of any color) are fatal. Remember your ancestors.	Spikes, pits, burners, thorns, lasers, and lava all deal 9,999 damage. Does not apply to projectile-based hazards (flamespewers, icicle shooters). Cannot be used simultaneously with Stone.
Stone	Damage from level hazards is quadrupled. Dream vaguely of your ancestors.	Spikes, pits, burners, thorns, lasers, and lava all deal quadruple damage. Does not apply to projectile-based hazards (flamespewers, icicle shooters). Cannot be used simultaneously with Rock.
Swarm	More enemies spawn. They will come for you. Your fate is known.	Twice as many enemies spawn.
Toxin	When the bonus timer runs out, you'll be poisoned until you die. No bonus chest.	No bonus chest appears. The bonus timer is replaced with the toxin timer, which counts down toward zero. When the toxin timer hits zero, the player takes 1 damage, and the timer resets to 10 seconds and continues counting down. The toxin timer stops upon reaching the boss gate.
Undying	Enemies have more health.	Enemies have double health.
Wrath	Enemies deal more damage. You've never looked so frail.	Enemies deal double damage.