Tagging (also known as tapping, both implying touching) in WvW is the same as it is in PvE: Doing enough damage to an enemy that you will get rewards after the enemy dies. The purpose of tagging as many things as possible is to maximize the amount of experience, WXP, karma, and loot that you get with the zerg. Some classes are better at this than others, but with the right skills, Elementalist can be among the best.
How hard do I need to hit?
The amount of damage that you need to do seems to scale with the amount of damage done by other players. If 2 players do about 50% of the damage, each, and you do 1% of the damage, you will not have hit enough for a tag. However, if 20 people all do about 5% of the damage, each, and you do about 1% of the damage, your damage will likely be high enough for a tag.
If you are in a party, it's slightly different. As long as your party members have done enough damage to get a tag on an enemy, a single hit should be enough for that tag to also count for you. Typically, WvW Commanders would prefer that you don't travel with the zerg as a party because it makes it so that boons are not evenly distributed. However, if you are still leveling, it can be beneficial for tagging purposes.
How can I tag in WvW?
The two main goals of tagging in WvW are:
- tagging enemies in zerg vs. zerg fights, and
- tagging the objective NPCs (Lords, Dolyaks, etc.).
When it comes to tagging zerglings, your priority is hitting as many of them as quickly as you can. This is useful not only for leveling but also for rallying. You can only rally off of a kill for which you have tag credit. In other words, someone that you barely tapped will probably not allow you to rally when they die. However, if you tag every opponent—and your zerg is capable—one of them is bound to die. You just have to stall (which Elementalists excel at with our Vapor Form downed skill) until you rally.
Typically, zergs move as a unit. This is why we call them zergs: they travel as a hivemind. This means that large ground-targeted AoE skills will allow you to damage a large amount of the zerg while still maintaining a safe distance. Running into the enemy zerg is a bad idea because none of your abilities can hit more than 5 people at a time. But more than 5 people at a time can hit you.
Because of the 5 target limit, simply having a large AoE hit isn't enough. You either need
- multiple hits in succession (each individual hit able to hit 5 targets), or
- some way of circumventing the target cap.
In the first case, Elementalists have abilities like Meteor and Glyph of Storms which cover an area of ground and continuously strike random positions on the ground. Each of these strikes can hit 5 targets at a time. In the case of Meteor, you can expand its radius with the Blasting Staff Arcana trait.
For the second case, any class can use siege weaponry. Arrow carts are an excellent siege choice for this. They can be deployed anywhere (including safely tucked on friendly walls), they can be fired rapidly as the first skill has a cooldown shorter than the amount of time that its AoE lasts, and it covers a large radius of AoE. Other good choices include cannons, mortars and even trebuchets (though long distance usage typically doesn't grant kill credit) when you have access to them and the enemy is too far away for an arrow cart to reach them.
Tagging objective NPCs
When it comes to tagging NPCs, the target cap is no longer an issue. Very rarely will there be more than 5 NPCs to fight at a time, so you are able to rely on any of your skills for tagging. So, let's focus on Elementalist abilities that are good at tagging.
When attempting to get a tag, you want abilities that:
- hit hard enough to count for a tag,
- hit many enemies simultaneously,
- hit fast so the enemy doesn't die while you are still casting, and
- have a long range so that you can hit while still catching up to the zerg.
Elementalists actually have a few utility skills that fit these qualities.
- Arcane Wave is a ground-targeted instant-cast AoE skill. It is very useful for tagging multiple NPCs, especially when the zerg is ahead of you. It also gives a guaranteed critical hit meaning you typically get your tags from a single cast.
- Arcane Blast hits just as hard as Arcane Wave (and is also a guaranteed critical hit) and is a 1500-range (longer than any of your other abilities) instant-cast single-target skill. It is great for hitting moving targets like Dolyaks, especially when the zerg is ahead of you.
- Ride the Lightning and Lightning Flash are great for catching up to the zerg and landing a hit. Both also do damage on contact and hit with about the same amount of damage as Arcane Wave and Arcane Blast.