Nightmare Mode

Nightmare Mode is a set of random challenges that can modify a mission's difficulty. Missions that are selected for Nightmare Mode have a black skull next to the mission's details. These missions are selected at random daily and only appear on planets of which every level has been completed. A Rare Nightmare mod with dual effects will be rewarded upon completion of a Nightmare Mode mission.

Challenges
All Nightmare Mode enemies are significantly increased in strength, and sometimes replaced with more dangerous versions. A Grineer Lancer will normally become an Elite Lancer. Multiple challenges can be applied on one mission. You could end up with Vampire, Timer, and No Shields challenges all at once for example. Lockers in Nightmare Mode do not drop ammo as of Update 9.3.


 * Vampire: Every Tenno's health will be reduced by 1.5% of maximum per second rounded down. This will not reduce your health lower than 1% of maximum. The death of enemies, including Infested Runners exploding, will recover 15% health for the entire Tenno squad.
 * Timer: The mission will now be timed, starting at between 3 and 5 minutes. The death of enemies will add to the timer.
 * Low Gravity: The gravity will be reduced approximately by half, causing less control of jumps. This also affects enemies and loot.
 * No Shields: Every Tenno's shields will be removed.
 * Shield Reduction: A weaker version of No Shields. Your shields will have an amount taken off. (200-400?)
 * Energy Drain: Gives zero shields in addition to draining energy. (33% chance to get this mode)
 * High Level Enemies: Enemies will have a higher level than normal.
 * Enemy Damage Buff: Enemies will cause greater damage amounts. (x2?)
 * Longer Reload: Reload Times are increased. (Possibly +50%)

Mission Rewards
Possible Rewards on completion include:

Known Bugs

 * Host Migration will sometimes cause enemies to revert to standard mission level, and special circumstances (Vampire, timer, gravity, etc.) to be removed. Mission will still reward as nightmare mode however.
 * The Vampire effect (and the Timer challenge) will take effect as soon as the mission begins, i.e. as soon as the beginning cutscene starts.
 * The scaling of the Affinity gained from enemies, seems to be lower than the original levels of the enemies in the mission, rather than scaled up to the new levels for Nightmare Mode. The scaling for the Credits reward is normal, though.
 * The screen goes blank before loading some missions (currently known mission Mars - Ultor).

Trivia

 * Nightmare Mode was added in Update 9
 * Nightmare Mode has been removed from Mercury as of Update 9.2
 * You can't do Nightmare Mode at rank 0.
 * You can't opt into the regular mission once you have unlocked the nightmare version.
 * Completing the same mission twice does not yield the same reward, similar to the Void.
 * More than 1 challenge mode can be applied with each mission, for example the vampire effect and the low gravity effect in the same mission.
 * Mission lobby screens for Nightmare missions have a red glow to them.
 * If not everyone in the lobby sees the mission as Nightmare mode from the solar map, only the ones who do should select the mission for it to be nightmare, otherwise the normal mission will start instead.
 * Nightmare mode missions will not appear on a planet before the whole planet has been completed.
 * Nightmare missions do not have a 1 minute end timer for a majority of players reaching the end.
 * You can join a mission with timer just seconds before it expires, thus failing it straight away.