How combat works

A fight is a sequence of rounds. Statuses tick first, then the attacker acts. Everything below is read live from the combat engine, which means these are the numbers the simulation actually uses, not a summary of them.

Nothing here needs reflexes. A battle is resolved from your build, gear, pet and potions, and then played back to you. What you brought decides it.

Dealing damage

Critical hit: Each point of LUCK adds 1.5% crit chance, then the total is dampened by your level - the same LUCK is worth less at 60 than at 10, so crit stays a choice instead of becoming automatic. A crit deals 1.5x damage. Hard cap: 50%.
Armor penetration: Ignores part of the target's armor before the damage formula runs. Every point of INT grants 0.2%, on top of the armor_pen affix on gear.
Damage ramp: Every 5 rounds BOTH sides deal +20% more damage, permanently and cumulatively. It exists so two tanky builds cannot stall forever - the longer a fight runs, the more it favours whoever is ahead.

Taking damage

Dodge: A dodged attack deals nothing at all - no damage, no on-hit effect. Each point of AGI gives 0.1%, capped at 20%. Assassins get a flat +10% and a higher 30% ceiling; rangers get +20% for the first 2 rounds only.
Armor: Reduces incoming physical damage by A / (A + 60 × attacker level). Because the attacker's level is in the denominator, the same armor value is worth steadily less as enemies scale - armor has to keep growing just to stand still.
Resistances: Physical and runic resistance are applied AFTER armor, as a flat percentage off what is left. They are the only defence that works against runic damage, which ignores the Logia passive entirely.

Damage over time

Bleed: 3 ticks, each dealing 40% of the attacker's attack power. Pure physical chip damage - it is not reduced again by armor once applied.
Burn: 1 tick for 35% of the attacker's attack power. Short and sharp rather than a long drain. Legendary fire pets pierce part of the target's resistance when they apply it.
Poison: 4 ticks at 12% of attack power each - the slowest DoT, and the only one that also cuts the target's healing while it lasts. Against a sustain build the heal cut is usually worth more than the damage.
Do DoTs stack?: No. Re-applying bleed, burn or poison refreshes the duration and keeps whichever tick is bigger - it never adds a second copy. Landing the same DoT twice from a weak source is wasted; landing it once from a strong one is not.

Control

Stun (shock): A shock does not guarantee a lost turn - it carries a chance, and the strongest shock on you is the one that rolls. Sources: the brawler's Bone Break (22% on hit), runic mage skills, earth pets, and the stun_on_hit affix.
Freeze: The mage's Ice Stasis fires once per fight when the mage drops below 25% HP and costs the opponent their next two turns. It is applied silently so it renders on the target, not as a stun on the caster.
Armor shred: Each stack strips 15% of the target's armor and they do add up, unlike DoTs. Total shred is capped at 85%, so armor can be gutted but never fully removed.

Healing & shields

Lifesteal: Heals you for a fraction of damage actually dealt, so it is worth nothing on a turn you were dodged or blocked. It comes from gear affixes, the guild tree and the Vampire's Mark potion - the potion version is capped to a few hits per battle.
Heal reduction: Poison and nature pets cut every heal you receive while active - lifesteal, potions and water pets alike. It multiplies the heal down at the moment it lands, so stacking healing against it does not out-race it.
Potions: Brewed at the Witch's cauldron and equipped before a fight. Basic potions are flat stat lines for the whole battle. Specials are one-shot or short-window effects - most are deliberately limited to an opening burst so a long fight cannot turn them into a permanent stat.
Dawn Shield: Absorbs damage out of a flat pool worth 15% of your max HP for the first 2 rounds. Unlike the pet light shield this is a bucket, not a percentage, and it works for both sides - a PvP opponent can bring the same potion.

Pets

How pets act: Your equipped pet acts on its own timer, every few rounds, as an extra on top of your turn - it never costs you an action. Rarer pets act more often (legendary every 3 rounds, common every 5). Only the equipped pet uses its combat skill; the rest of your collection contributes stats.
Light pets (shield): Applies a damage reduction of up to 45% plus 1 round of immunity to stuns. The shield can never cover more than 67% of the pet's own cooldown, so there is always a round where you are exposed - it is a defensive window to play around, not a permanent buff.
The other four elements: Fire strikes and burns. Nature strikes and poisons, cutting the target's healing. Earth strikes and rolls to stun. Water does no damage at all and instead heals you on its timer - on a legendary as a share of your max HP, otherwise as a share of the HP you are missing.