Tyroxin/Buddelkiste

Elementalist

Build	Notes
Condition	Check for signets. If they have Signet of Earth and a couple of other signets then they are playing a condi bunker spec with good sustain but low to medium damage and poor mobility. Suitable for smaller fights such as 1v1s Elementalist: Tempest profession: they may povide tome support as Tempest.
Condition (Sidenote)	Weaver profession: Sword, Signet of Restoration on their buff bar. This is the most common Weaver build. Fire Weavers will be looking for 1v1s and other smaller skirmishes. Good sustain, medium damage, uses Primordial Stance to burst.
Fresh Air	Elementalist, Weaver profession: Scepter, no signets, not even for the healing slot. High mobility, decent CC, big burst damage but very squishy. Plays as a roamer, wants to +1 fights and finish targets in seconds. Ranged casters. Weaver: Scepter/Focus, usually no signet in the heal slot as they play Glyph of Elemental Harmony. Freshweaver has excellent ranged burst damage, very high combat mobility, good CC. Rather poor sustain, especially against conditions. Fresh Air buff's often active on their bar, easy to tell in combat. Roams the map, seeks to +1 fights.
Lightning Rod	Weaver: Dagger/Focus, this is a melee focused CC-machine centered around the trait Lightning Rod. Much more likely to have a Signet of Restoration + Signet of Air combo than S/F Fresh Air. LR builds are easy to spot in combat as you'll see frequent lightning strikes whenever they CC someone, which also applies Weakness to the target. Counters For them the best defense is a good offense, they don't have much sustain but their CC and Weakness spam keeps their enemies at bay. Stability is very useful to have against them.
Power Sidenoder	Tempest: check out their buff bar and weapons. Signet of Restoration is a major giveaway that they're not actually support, as supports would run "Wash the Pain Away!" for group healing. If there's also a Signet of Air then it's probably some sidenode 1v1 power spec.
Support	Elementalist, Tempest: Staff or a Dagger/Focus set (and no signets). Inspect their weapons if they are on your team. Staff is the only core Ele weapon they carry on their backs so that one is the easiest part to spot. Tempest Tempest is the go-to support spec of Elementalists in PvP, at least 9 out of 10 are going to be playing support so even from the elite spec icon you can make an educated guess. These tend to be Dagger/Focus or Staff builds. They can share auras, boons, do lots of healing and offer AoE cleansing for the team. Depending on their build they could be weak to either power or condition damage. If they are in Earth Attunement and you see a Stone Heart icon on the buff bar that means they run the Earth build which has lower cleansing but better defense against power damage.
Other	Tempest: despite being their elite spec weapon, Warhorn is not popular on Tempest, at least in PvP. The only builds that run this tend to be Air magic builds, power or hybrid like the D/Wh Shocking Aura spec. This offhand is the only way of knowing outside combat.

Engineer

The vast majority of Engineers in PvP are playing power-based specs focusing on burst damage with minimal sustain. They have plenty of unique buffs from traits and signets that could help us identify what we're up against.

build	Specs	Notes
Power	Engineer/all	check their buff bar for Explosive Entrance, this means they are running Explosives. Usually a sign of a squishy but high damage power build.
	Scrapper	if they have Explosive Entrance expect a low sustain high damage build with Grenade Kit and/or heavy point-blank AoE from gyros.
	Holosmith:	expect Holosmiths to run high damage, low sustain builds. Their bunker builds are dead and condi was always niche. They'll roam the map and attempt to +1 fights, but better ones could also take some 1v1s. They're generally weak to conditions, but the Tools variant fares better against them. You can spot a Tools holo from their frequent but short duration Vigor procs or Kinetic Battery charges.
	Mechanist:	once again, keep an eye out for Explosive Entrance. Low sustain, high mobility, moderate ranged damage. There aren't a lot of Rifle Mechanists in ranked these days however.
Condition	Mechanist:	check their buffs for Superconducting Signet. These are midrange jack-of-all-trades, master of none specs. Can perform a variety of roles, their damage depends a lot on their Mech and the Superconducting Signet. Low sustain, high mobility, decent damage in medium range to close range. Check out this build for more details.
Bunker	Scrapper	if the Explosive Entrance buff is missing there's a chance that they are playing a bunker build. Be careful in melee especially when contesting a point as they're still able to do high damage by overlapping various AoE skills such as Acid Bomb and Thunderclap.
	Mechanist:	if none of the above mentioned signs are present, assume it's a bunker build. Low damage, medium sustain, sits on node and either stalls or tries to win over time. Destroying their Mech reduces their sustain and takes away their killpotential.