Which Weapon gets the Kill

When you have two weapons, a main-hand and off-hand, which weapon gets the credit for the kill? Is it based on percentage of damage? The killing blow regardless of total damage dealt? Or do they both get credit as long as both dealt damage to the creature? What if you switch during combat?

AFAIK the killing blow only - be it through direct damage or condition ticks.

Which is why it is a royal PITA to do with off-hands.

Yeah, it's the killing blow. To complicate things, though, I think that conditions can mess with that, as can sigil effects (ie. the fire AOE from Sigil of Fire) and traited effects.

As said above, the killing blow gets the count.So if you want to kill something with conditions of a offhand weapon, its a good idea to get rid of autotargeting, so enemies can burn or rot to death.There are occasions of offhand weapons being used in more offensive forms. Which makes getting the accrual kill more easy.

Traits like

https://wiki.guildwars2.com/wiki/Bloodlust

are the absolute worst when it comes to this, because it will very often cause your Main Hand to "killsteal" your Off-Hand since those stacks are most likely gonna build by your auto-attacks.

Usually the more reliable way to get off-hand kill credit is to unequip the main and fight ambients. (And be careful which traits/sigils you have; there are some wonky mechanics in which a lot of things give staff-kill credit.) There are more PvE areas now with ambients than there used to be, and a couple of infinitely-respawning locations in various personal stories.

Still horribly tedious imo, though, which is why I haven't bothered with them.

A bit of clarification:

1. For the weapon mastery achievement, the weapon that hits last and actually kills the enemy gets the kill credit. I.E. a revenant is running sword/axe. If his skills 1, 2, or 3 kill the enemy, the sword gets credit. If the last swing that kills the enemy is skill 4 or 5, it's an axe kill. If the same rev had sword/shield, he would NEVER get kill credit for the shield, because a rev has no offensive shield skills.
2. Utility skills and class mechanic skills don't contribute to the weapon mastery achievement. Same goes with kit skills (i.e. engi Flamethrower or ele Ice Bow) and class mechanics (i.e. thief stolen skills, necro shroud skills, engi toolbelt skills). Damage from pets, retaliation, runes and sigils also does not count, regardless of the equipment it is in. An exception is the Warrior burst skills. They give credit for the weapon type that the skill is based on.
3. I honestly have no idea how condi is dealt with in relation to weapon mastery. I'd avoid it if possible while working on the achievement. ESPECIALLY if both main and off-hand weapons inflict the same conditions.

@"CaelestiaEmpyrea.2617" said:

2. Utility skills and class mechanic skills don't contribute to the weapon mastery achievement. Same goes with kit skills (i.e. engi Flamethrower or ele Ice Bow) and class mechanics (i.e. thief stolen skills, necro shroud skills, engi toolbelt skills). Damage from pets, retaliation, runes and sigils also does not count, regardless of the equipment it is in. An exception is the Warrior burst skills. They give credit for the weapon type that the skill is based on.

https://wiki.guildwars2.com/wiki/Weapon_Master

Some bundles and utility skills count as a specific weapon type. For example, the golem suit in Air Drop story mission counts as a hammer, and the Arcane skills count as a sword. Some, such as conjured skills like Lightning Hammer and Magnetic Shield do not count towards anything.

The following Necromancer minions count towards Scepter: Blood Fiend, Bone Fiend, Bone Minions, Shadow FiendThe following Necromancer minions count towards Hammer: Flesh Golem, Flesh Wurm, Reaper's ShroudThe standard/F1 attacks of the following Ranger pet families count towards Staff: Moa, Bear, Feline, Canine, Drake, Bird, Spider, Armor Fish, Jelly Fish, SharkThe standard/F1 attacks of the following Ranger pet families count towards Hammer: BristlebackSupposedly, some Ranger pet counts towards Greatsword.It’s unconfirmed but players did report Engineer Turrets and Kits racking up Staff kills.

Disguises, transformations and environmental bundles can also count towards a specific weapon without you realising it.

@Haleydawn.3764 said:

@"CaelestiaEmpyrea.2617" said:

2. Utility skills and class mechanic skills don't contribute to the weapon mastery achievement. Same goes with kit skills (i.e. engi Flamethrower or ele Ice Bow) and class mechanics (i.e. thief stolen skills, necro shroud skills, engi toolbelt skills). Damage from pets, retaliation, runes and sigils also does not count, regardless of the equipment it is in. An exception is the Warrior burst skills. They give credit for the weapon type that the skill is based on.

Reaper's Shroud on Necromancer counts as Hammer as well.

Death Shroud on core Necromancer counts as currently equipped weapons (1-3 counting as mainhand, 4+5 counting as offhand) for your active weapon set when you enter Shroud.

@"CaelestiaEmpyrea.2617" said:

3. I honestly have no idea how condi is dealt with in relation to weapon mastery. I'd avoid it if possible while working on the achievement. ESPECIALLY if both main and off-hand weapons inflict the same conditions.Usually it doesn't count at all, so when working for weapon kill achievements, you definitely don't want to use condi.