Level Drain

In a Class and Level System, as characters gain levels, they become more powerful. Some games have enemies (usually of the undead variety) which have the ability to take these levels away from a character, which has the effect of weakening the character, usually described as an attack that drains the character's Life Energy. Since it involves stealing life force, with undertones of Necromancy, users of this power are almost always evil or "grey" characters.

If there is no way to easily gain these levels back, enemies that can do this often take on the status of Demonic Spiders, especially if they appear in groups and can drain more than one level per shot. Characters who lose all their levels this way typically die, and often come back as the creature that killed them, or a subordinate creature under the control of their killer, particularly if the creature was undead.

Do not confuse with a Drain Level, which is something entirely different.

Tabletop Games

 * Dungeons & Dragons, as you might expect, is the Trope Maker and Trope Namer. Under most circumstances, the only way to defend against level drain was by making a saving throw against it, or by using magic items or spells that protected you against the drain.
 * In the older games (and the retroclones based on them), if you lost a level to level drain, it was gone for good, and the only way to gain it back was the hard way, since restoration magic was out of the reach of spell casters until the highest levels. The earlier games also operated by having every gp of treasure earned count towards XP, so you didn't have to slog through tons of monsters in order to get back into tip-top shape (in addition to being a better way to survive the low levels due to the low HP that first-level characters had).
 * In Advanced Dungeons & Dragons, there was no save. If an undead creature hit you, you got level drained and that was that. Worse, energy-draining touch attacks ignored armor, and the only real defensive spell against such attacks, Negative Plane Protection, only shielded one character against one level of drain. In practice, the only real defense against level draining undead basically boiled down to "don't let them get near you, ever."
 * A First Edition spell called "Energy Drain" had the same Level Drain effect as being touched by an undead.
 * Third Edition introduced the concept of "negative levels," which was basically temporary level loss that you then had to make a Fortitude save against at the end of the fight for every level that you "lost" this way. If you made it, you got the level back, but if you failed the save, it was gone for good and you had to gain it back the hard way.
 * Fourth Edition did away with level drain entirely, instead having monsters that originally level-drained you (such as wights and wraiths) instead inflicting the Weakened condition on you (which simply halves the damage that you deal in combat until you make your saving throw to end it), immobilizing you (you can't move from your space unless you teleport until you make your save), taking away healing surges, and so on.
 * Pathfinder finally eliminates the issue, by making almost all energy drain a temporary state. Failing the save to remove the negative level just meant you kept it for another day.
 * Another game by TSR, Gamma World (1st Edition), had the "De-Evolution" mutant ability. A "Sage Advice" article in Dragon Magazine confirmed that if a mutant with that ability showed up in a Dungeons & Dragons campaign, it would cause Level Drain like an undead monster.

Action Adventure

 * This is a major game mechanic in Cave Story. You level up your weapons by collecting powerups that enemies drop, and getting injured by anything will lower your weapon level.
 * Same for the original PC-88/MSX version of Valis: The Phantasm Soldier.

MMORPGs

 * RuneScape has many monsters, especially quest monsters, who do the temporary sort of draining, and there's even 'disease' from special undead, which hits a random stat for 10 to 1 levels, and there are potions to restore levels and cure disease, as well as jewelery that takes the disease for you.
 * Kingdom of Loathing features items, equipment, and familiars that can do this to monsters. On the other side, there are also items and equipment that can add levels to the enemy, in order to boost their power (and the Experience Points paid out for defeating them). A few rare items can do this to your own statistics, too.
 * In the early days of EverQuest, you could fall into a "death loop"—If your spawn point was near a group of monsters, they'd keep killing you repeatedly. What made it even worse was that you'd spawn without your equipment, making you even easier to kill. You could easily lose a level or more this way. As you can guess; this was a Scrappy Mechanic.

Roguelike

 * Many Roguelikes, such as Nethack, have this as just one of the many dangers that your character can face. Yes, they're Nintendo Hard.
 * The original Rogue had one of these too, the Wraith. It drained a level but left you at the maximum experience of the previous level, so the experience from killing the wraith would make you go up a level again (though with minimal experience for it). Too bad if you got drained twice before killing one, though.
 * Angband has not only various levels of EXP drains, but also melee attacks that lower any or all of your stats.
 * The original Diablo had yellow zombies, which permanently reduced your max HP every time they landed a successful hit.
 * Pokémon Mystery Dungeon has Doom Seeds, which lower your level by one if you're hit by one... or eat it.
 * Chocobo's Dungeon 2 not only has level down seeds your big yellow bird can eat, but level down traps and a whole family of monsters (Vampire/Lich/Demi-Lich) that can drain levels as an attack. For some strange reason, this is partly balanced out by having level up seeds and traps.
 * In Azure Dreams, there's a somewhat Grim Reaper-esque monster called Clown on the lower levels of the tower. Its special ability is a spell that drains a level from your PC or one of your familiars. Killing it brings the level back. However, this is treated as a new level-up, so all the EXP you collected mid-level are gone.
 * Izuna Legend of the Unemployed Ninja features an enemy that can drain one level from you. When you defeat it, you level up, bringing you back to your original level.

Role-Playing Game

 * There were two kinds of Death monsters in Gauntlet (1985 video game) Dark Legacy: a Red Death which drained 1000 hit points, or a Black Death that would drain one level. Thankfully, the halo accessory meant you could drain from these Deaths, and draining from the Black Death would make your character gain a level, no matter how much XP they needed. This made Level Grinding very quick.
 * Final Fantasy V had several enemies and powers that cause level drain, though thankfully it's all temporary.
 * Not to mention; you can actually do it on the enemies, too. Often you can use abilities such as Darkshock (Which halves the target's level and rounds if necessary) or Level 2 old (Which gradually delevels them). This makes abilities that attack the opponents via levels (Level 5 death, Level 4 Holy) much more feasible.
 * Final Fantasy VII had this as a handicap in the arena fights in the Golden Saucer. It reduced your level by five for the remainder of the duel. This was actually one of the less nasty penalties, at least it didn't shrink you or worse, turn you into a frog.
 * Final Fantasy VIII enabled one GF to learn a LV Down ability for the player to use, which could be used repeatedly to make any non-boss enemy stupidly easy. It had a LV Up ability, too, for those who think scaled leveling of enemies just isn't hardcore enough.
 * It's also yet another Game Breaker in a sea of many that the game lets you use at your leisure. Level the monsters up, draw their now-updated magic, level them down again so that you can either kill them in one hit or raise the effectiveness of Break.
 * Persona 2 has the "Prophecy" spell, which resets a Persona's rank to 1. Given that a Persona's spells and stats come mostly from gaining ranks, and going from rank 1 to rank 8 often takes several hours of Level Grinding, this can be aggravating.
 * In Demon's Souls, there is the Soulsucker spell, which is used by one of the bosses in the game and can also be learned by the player. It has a slow casting time, but a hit from this will drain the player's Soul Level.
 * Slow casting time (and telegraphs the entire cast), melee range, roots the caster in place and costs practically all their mana. If you get hit by this, you are probably Too Stupid to Live
 * In the .hack// series, the power of Data Drain can result in an NPC character losing character levels and distorting into a very weak monster. Player characters hit with Data Drain can have their human player be digitized, imprisoning their mind in the game and placing their body into a coma.
 * In .hack//G.U. and .hack//ROOTS, the entity Tri-Edge Data Drains the characters Shino and Haseo, sending the former into a coma and transforming the latter from a high level character to first level with no inventory or member address list.
 * There's at least one already difficult boss in The Legend of Dragoon (The Grand Jewel) that can take away levels from your current attack, and they will stay that way until you gain them back the hard way. In a part of the game with several boss fights in a short period of time, no less. There are also several bosses (including, again, the Grand Jewel) that make your dragoon abilities useless, which can be seen as leveling them down for the battle.
 * In Wild ARMs 3, there's an enemy in The Abyss called the Vampire. While it doesn't lower levels, their Kirlian Buster attack lowers MAX HP. This can be very bad, considering they appear around the middle floors and can hit with it often. On the other hand, they only use it as a counter to Arcana, but they counter physically attacks with nastily high powered hits...
 * The Kirlian Buster returns in Wild ARMs XF as one of the earliest enemy Arts one can encounter. However, since the game is an SRPG and the spell's affect isn't permanent, the Kirlian Buster hardly poses any threat to the player. And the pathetic success rate of the spell itself doesn't really help.
 * While they don't affect the characters' levels, several endgame bosses in Golden Sun: The Lost Age and Dark Dawn have moves that shut down a character's Djinni, and a couple of them can shut down all of the Djinni in the active party. Doing so reverts the characters into their significantly weaker base classes. Fortunately, Djinni do return in battle, but only one of each character's 9 Djinni comes back each turn - especially problematic because most Revive spells and all group healing spells require classes with four or more Djinni of a particular element.
 * In Kingdom Hearts 358/2 Days, one status ailment actually deleveled your character. It was only temporary, similar to Final Fantasy V.
 * Games in The Elder Scrolls series will generally lower a random skill when you're put in prison. There are also various magical effects that temporarily drain the gains and means of increasing in level (health, magicka, fatigue and skills).

Shoot'Em Up

 * All damage is like this in the flash game series Bubble Tanks. Then again, the game does provide an Anti Frustration Feature where they provide you with experience-giving Pinata Enemies should you get hit too often.

Turn-Based Strategy

 * A certain monster in Disciples II did this and also brought the target down one Evolution Level.
 * Final Fantasy Tactics has a "level down" trap that you can use to abuse the leveling system for ungodly powerful stats (though most players generally don't bother).
 * In Makai Kingdom, any enemy with a hammer/mallet can steal a level with every hit. Sure it's easy to get back, but it's downright frustrating in the early levels. Also, you do not have such an ability, even if you have the best mallet in the game, putting this somewhere between My Rules Are Not Your Rules and Secret AI Moves.

Web Comics
""These hatchlings are a good start, but they should drink healing surges and eat five levels.""
 * Tycho instructs Gabe on how to make his monsters more deadly.


 * This is Xykon's favorite form of attack in Order of the Stick. He's used it on multiple occasions to take down other epic spellcasters.