Damage Increasing Debuff

A negative status ailment that makes its subject take more damage from whatever hits them.

Comes in three different flavours: Some effects of this type do this directly by changing taken damage by some percentage (reducing the amount of hits an enemy can take in a way sometimes functionally identical to a Percent Damage Attack). Others reduce Damage Reduction, resistance or armour value. There's also a rare type of this which adds a fixed amount of damage to every hit.

All of these are fairly different each, but they have one thing in common: Every hit they take while in this state hurts a lot more. This type of effect (especially the defense-lowering kind) is often the key to beating resilient enemies. The way to exploit this For Massive Damage differs depending on type: the strongest attacks should be used while the target is afflicted with a percentally-functioning Damage Increasing Debuff. "Per hit" types especially increase the power of the Spam Attack or a Gradual Grinder's Damage Over Time attacks, and are quite rare in games with realtime combat or a speed stat since such a modifier tends to be unfairly powerful if you can get many hits in short time.

If inflicted physically, this is often a speciality of martial arts. If inflicted magically, this tends to be a curse or some other sort of Black Magic. Might be the side effect of channeling spells, like in Final Fantasy Tactics.

Compare and contrast a Critical Hit or elemental weakness exploitation, which usually mean increased damage for a single attack. Compare and contrast a Status Buff Dispel against shield spells. Compare Break Meter. Compare the defense-debuffing type with Armor-Piercing Attack. Contrast a Status Buff or trait that increases the damage dealt by someone, and also contrast a debuff decreasing evasion.

Note that this is about a debuff that increases the damage taken by its subject, not about a damage-dealing debuff whose damage gradually increases.

(For those who don't know: The term "debuff", as opposed to a positive Status Buff, is mostly used discussing video games and refers to a temporary ailment with negative effects for its subject.)

Tabletop Games

 * The Pokémon Trading Card Game has at least a dozen cases of this. This includes the rare "extra damage per hit" type: For instance, Machamp Lv.X has an effect, "No Guard," that increases damage by 60, both done by and done to Machamp.
 * Magic: The Gathering has Wound Reflection and Curse of Bloodletting, which double your opponents' pain.
 * Warhammer 40,000 has the "curse" psychic power, which makes the target more easily wounded.

Tabletop RPG

 * Dungeons & Dragons 2nd Edition supplement The Complete Psionics Handbook. The Double Pain power greatly reduces the target's pain threshold and causes them to take double damage from all attacks for 10 minutes. However, the extra damage is temporary and can only cause unconsciousness rather than death.
 * In 4E, there is a game mechanic called "Vulnerability" where creatures have negative effects dealt to them when hit by certain damage types (usually a fixed extra amount of damage, but occasionally other debuffs like disabling regeneration or being slowed). There are several powers that allow you to impose these vulnerabilities upon enemy targets.
 * Shadowrun:
 * When a victim of the drug Hyper takes any damage, they automatically take an equal amount of Mental damage as well.
 * The Reduce Body spell basically reduces the defense stat.
 * Champions. The Drain and Transfer powers can be used to reduce a target's defenses, making the target more vulnerable to subsequent attack.
 * Vampire: The Masquerade: A side-effect of some uses of Obtenebration, a main effect of one Quietus power, is decreased defense.

Action Adventure

 * In Bastion, some idols cause you to take extra damage when they're active.
 * Cripple in Distorted Travesty temporarily decreases the defense of an enemy afflicted with it.
 * In Kid Icarus: Uprising, there are enemies that can inflict Weaken status on you. This temporarily shrinks your lifebar to half its size, making any hits taken deal twice as much damage. You can Weaken other players in multiplayer matches, if your weapon has the effect or you use the Weaken Attack power.

Eastern RPG

 * Final Fantasy:
 * While charging a spell or an attack, units in Final Fantasy Tactics take more damage from all attacks.
 * The "Oil" status in Final Fantasy XII triples the damage incurred from Fire attacks.
 * The recurring "Expose Weakness" spell decreases defense:
 * Final Fantasy XIII has the Deprotect and Deshell statuses, which reduce the target's physical and magical defence, respectively.
 * Final Fantasy XII has three Technicks that work this way: Addle lowers the foe's Magick resistance, Shear lowers the foe's physial damage resistance, and Achilles adds an additional element weakness to the foe, increasing damage dealt if of that element.
 * Final Fantasy VIII has the "Vit. 0" effect caused by the Meltdown spell, which sets an enemy's physical and magical defense to zero.
 * The remake of Final Fantasy IV has the "Cry" ability that Porom can use, which decreases the defense of all enemies. You can later give this ability to other characters; hilariously, the preferred recipient is often Kain (since he has so few other abilities), meaning you can take the series' Memetic Badass and make him cry like a little girl on command.
 * Pokémon has both general and element-specific examples of this. Leer, Screech, Tail Whip, and Tickle reduce the target's Defense. Fake Tears and Metal Sound reduce the target's Special Defense. Superpower deals high damage but reduces the user's own Defense. Close Combat, Shell Smash, and V-Create reduce the user's own Defense and Special Defense.
 * In The Reconstruction and I Miss the Sunrise, if a side gets Rushed/loses the Zone of Control (which is mostly same thing known by a different name in each game), they take more damage while also inflicting less. Also, poison (while otherwise being your standard HP sap) percentally increases the damage of Moke's Toxic Shock spell.
 * In Radiant Historia, enemies launched into the air take a percentage of the damage they took while in air when hitting the ground. Characters who used the Change command take more damage until it's their turn.
 * The crisis cast of Aquabeam in Last Scenario lowers the victim's magic defense.
 * Defense-lowering debuffs are common in the Epic Battle Fantasy series: Screamer, Beholder, Secret Weapon, Natalie's Limit Break... They overlap with a Status Buff Dispel against defense buffs, as using a defense-lowering attack against a shielded enemy will just remove the buff, and shielding someone with a defense debuff will only cure that debuff.
 * Sap/Kasap in the Dragon Quest series halve the defense of one enemy/all enemies respectively.

Western RPG

 * Both Dragon Age games have Mark of Death, which effectively boosts damage to a target from anyone by 20%. Dragon Age 2 has the Brittle status effect, the Hex of Torment and the Wounding Arrow.
 * Petrification in Dragon Age II, inflicts the percental debuff, and, once upgraded, decreases defense. Before, it increases it.
 * Diablo 2 features the "Amplify Damage" curse, which reduces physical resistance by 100%. In the majority case that the enemy had no physical resistance to begin with, this means double damage.

MMORPG

 * City of Heroes: Most attack powers have debuffs as side-effects, including this. In particular all Sonic attacks.
 * Deleveling an enemy in Kingdom of Loathing will reduce their damage absorption, along with their attack power.
 * And during the level 12 quest, some enemies can inflict a status ailment on you that increases damage taken from their element.
 * Guild Wars has all flavors of these, in various hexes and conditions.

First-Person Shooter

 * In Borderlands, enemies aflicted with a Corosive elemental effect suffers additional damage from all sources, including subsequent Corosive effects.
 * Team Fortress 2: Being covered in Jarate or cursed by the Scout's Fan O' War turns all taken hits into mini-crits, increasing their damage by 35%.

Turn-Based Strategy

 * In the Fire Emblem games set in Tellius, Luna is a special attack that acts as if the target's defense was actually half its current value. Aether, which only Ike can obtain, turns one attack into a healing Sol attack and a Luna attack in quick succession.
 * In Age of Wonders 2 handicaps inflicted by attacks include Cursed (from attacks with Death damage), Poisoned (Poison damage) and Vertigo (Holy damage); these are defense reduction overlapping with elemental weakness. And of course, there are many debuff spells. Age of Wonders: Shadow Magic adds Shadow Sickness, forced on most normal units visiting Shadow World without protection.
 * The Frozen status ailment in Odium, in addition to paralyzing the victim.
 * Mazinger Z's Rust Tornado has the effect in some Super Robot Wars games. In the Super Robot Wars Original Generation series, the Armor Breaker and a few enemy-only attacks decrease the target's armor stat.

Real Time Strategy

 * StarCraft has the acidic attack from Zerg Devourers.
 * Star Craft 2 has the Corruption ability, which makes their target receive 20% more damage for a few seconds.
 * Warcraft3:
 * The Berserk status allows to user to attack much faster, but it takes a lot more damage (in %).
 * Faerie Fire, an autocast move, removes some armor from the target and allows the user to see that unit until the effect fades.
 * One armor-boosting magic aura is often modified in custom maps to decrease nearby enemies' armor.
 * Using Banish on a unit makes it immune to physical attacks, but greatly reduces its resistance to Magic-type attacks and spells. As it also slows the target considerably, it's risky to use it on your own units.

Tower Defense

 * The Evileye Tower's 'Radiation' effect in Cursed Treasure increases damage taken by those afflicted with it by a percentage. Initially, it's 25%, but you can upgrade this up to a 50% increase.

Other

 * Clonk:
 * The Curse of Pain in the Fantasy pack makes its victim take double damage.
 * Battlecry and Swarm in "Keepers" percentally increase their subject's damage. Battlecry's power depends on its user's skill level, while Swarm consists of many locusts, and the effect strength depends on the amount of locusts that reached their target.
 * In League of Legends Kayle and Swaim have abilities that cause an enemy to take more damage from them for a short time, while Vladimir's ultimate causes enemies hit by it to take more damage from anyone. There's also a very large number of spells and items that use the indirect variant of reducing armor or magic resistance.

Non-game examples

 * In the One Piece series there's Oil: when a character covered in oil is hit by a fire attack or explosion he suffers a lot of damage (unless it's Ace).
 * Aetheria Epics has Argo's "pugilism" debuff technique.