Debuff
Hex
Champions under Hex debuffs take damage whenever their allies do. The damage from Hex debuffs ignores Champions' DEF. The original targets all take full damage.
Champions under Hex debuffs take 2% of AoE damage inflicted on their allies, and 10% of single-target damage inflicted on their allies.
Champions under Hex debuffs only take extra damage from direct attacks on their allies, not lasting effects (like buffs or debuffs) - for example, damage from Poison, HP Burn, Bomb debuffs, Reflect Damage buffs, etc.
What the game's own status effects screen says
In the game data this effect appears as Mark.
Champions that apply it
27 champions have a skill that applies Hex, according to the effect lines in the game data. This lists who applies it, not how reliably: chance, duration and resistance are on each champion's page.
Akemtum
Aratheia Corpseflower
Cleopterix
Cromax Moonblood
Holguk of the Hallowsights
Holsring
Karilon the Ringer
Lysanthir Beastbane
Mad Hatter
Maranix
Michinaki
Mithrala Lifebane
Packmaster Shy'ek
R. Nergigante Archer
Ruel the Huntmaster
Searsha the Charred
Skorid the Halfspawn
Soulless
Stonebound Thisbe
Teela Goremane
The Calamitus
Thea the Tomb Angel
Thylessia
Urticata
Valkanen
Vildrax
Yumeko
The description is the game's own text. It has not been tested in battle here, and the game's wording can be loose (for example about numbers that differ between versions of an effect). See Data quality for what has and has not been checked. Found a mistake? Use "Report a problem" at the bottom of the page.