As a disclaimer I do want to point out that I ran through all of the tiers, except for Liadri, as my Ranger. I utilized a Berserker build that used both Signet of Stone and “Protect Me!”, and swapped to a condition-heavy trapper build when I needed to keep foes away from me but still hurting. At Liadri I had to swap to my Guardian and in that section of this guide it will explain the build I used.
It's good to note that two foods are very helpful for this content: Bowls of Curry Butternut Squash Soup (for when I really needed to burst down a boss) or Bowls of Orrian Truffle and Meat Stew (for when I needed to dodge often).
Dodge when he does his wind-up and use ranged abilities with cripples or chills. Generally just keep him at a distance.
Easily kite-able with cripples and chills. Just keep him slow and you can easily get the full ten stacks for the achievement without issue.
This one practically requires stability. Burst her down as quick as possible to avoid dealing with multiple tornados, or stick a mass of conditions on her and focus on avoiding the tornadoes as she ticks down.
Suriel the Blazing Light
The main strategy to this fight is kite her into the darkness circles, burst her down when she's vulnerable and keep a close eye out for when she stops spamming her short range attacks so you can dodge, move to a shadow circle or pop an invulnerability skill.
It's best to stay near a darkness circle until she pauses to cast her massive one-shot skill so that you can move quickly to it's safety and not have to scramble for one.
Kite with cripples and chills, and use invulnerability or dodge when he gap closes.
Use a skill that gives you speed, or gives you haste so you can collect about 10-15 orbs to give you a substantial enough boost to damage to burst him down. Having both, however, as well as a movement skill should give you enough time to gather a full stack of the orbs for the achievement.
Leaving the flame circles is not an option until they fade away, so just keep a close eye on the slow moving fire waves and you should be able to maneuver between them without issue. When the circle goes down strafe in a clockwise circle (until another flame circle pops up) while ranging him.
The crew of the pirate ship Ravenous
You'll want one weapon set that is a little more AoE/multiple target friendly, then one for single target destruction. You'll want to take out Stitches → First Mate → Master Gunner → Captain. Stitches so she doesn't keep healing the others, the First Mate second because of the strong burst it has, Gunner for the frustrating AoEs and conditions and the Captain last because he's your only choice left!
If you don't care about the achievement: AoEs and weapons that target multiple mobs so you can always hit the Subject 7 among it's mass of oozes.
If you want the achievement I suggest pushing/pulling Subject 7 out of the middle of the group and focusing it down with a melee weapon. Utilize projectile negation (Guardian's Shield of the Avenger or thief's smoke wall) to ignore the other oozes while you hit Subject 7.
Basically you just need to stay in his face by using gap closing skills (if it's not a teleport, I recommend popping an invulnerability skill as you gap close for all the bombs) and bursting him down while you are close. You can either dodge through his sniper shot, or invulnerable through it.
Strugar and Chomper
You want to steal the meat away from Chomper until you have about five stacks of the buff, so you'll want to use cripple and chill skills to keep Chomper away from the food. After you get buffed up focus down Chomper with Conditions or a massive burst build, then smack down Strugar.
Liadri the Concealing Dark
I won't lie to you, this is a very tough battle that takes a lot of learning how the AoEs work and how you should be attacking and cleansing conditions.
The build I ended up using to crush her was with a Berserker Guardian 3-shout build utilizing 0/0/30/30/10 (traiting for shouts to remove conditions and boons heal) with Shelter, Renewed Focus and Staff as my only weapon.
You will see in the screenshots how I moved during phase one, to make it fast and to dodge as little as possible and always make sure you pop the Rifts when you see them spawn, or they can entirely screw up your groove.
Phase Two I move myself towards the center of the dome and run in a clockwise circle to offer the least amount of distance to get to the next safe spot. She will hit you with bleeds, weakness and cripple so you will want to use a shout when you are afflicted. Staff was the best weapon for me, here, so I could hit through the clones of her and make sure I kept hitting her during my sharp turns. This is the phase where I would use Renewed Focus and Shelter as panic buttons, but also to clear out the clones so they weren't massive pile-ups.
Finally a great place I found some advice was this thread on the GW2 Reddit. Go there to add more voice to it and find out some specific details for the various classes.