Burn
You've set them alight. A burning foe loses HP every second until the fire goes out, and you don't have to do anything to keep it going.
In detail
Damage over time on the enemy, laid by Fire proc charms such as Ember Coal and by Sinmara's Pyre-Heart, which rolls on any hit rather than only Fire matches. The total is about 50% of the hit that triggered it, paid over 5 seconds at one tick per second, and it can land the killing blow. Re-applying refreshes the duration and keeps the larger per-tick number. Leváteinn's Edge detonates a burn on contact: it pays out every tick still owed at once, then applies a fresh burn sized on the damage it just dealt. That front-loads damage the enemy was already going to take, so it only nets more when the burn would have been cut short. Bosses, echoes and mini-bosses resist debuffs at about 60% effectiveness, so a burn does roughly 60% of its damage to them.
More in glossary
From the current development build. Content and balance may change before release. This public reference includes discoveries and does not reflect your personal unlocks.