Enemies: Dredge and some elementals.
Video guide [KING].
Current record (Bombs): 48.
Current record (Turret): 49.
You start in a huge area with 4 locked gates, 4 pressure plates, 3 cages and lots of dredge. The idea is to stand on pressure plates to open gates for other players. At the end there is a console which opens all gates permanently.
Go up on the ramp on your left to get on the first locked gate. Killing aggroed enemies is highly recommended because then you can make up a plan and take a look around the area without any pressure. However enemies inside cages respawn so just randomly rushing somewhere is pointless and will just get you killed.
The first gate is opened by standing on a pressure plate which is located on the first cage. The first cage can be reached by simply going to the left path. Only one player should do this because the gate immediately closes when you step off the plate. If additional players help with the first gate then you will have problems with the next gates.
All cages have lots of enemies so prepare accordingly. Take mobility so you can get it and out fast and defensive skills so you can tank longer. Stealth is very helpful and can be acquired from consumables like Harpy Feathers (consumable), Ash Legion Spy Kit or Order of Whispers Spy Kit but is not required. As a gate opener your job is to stand on the pressure plate until rest of the party gets through the opened gate.
If you aren't the gate opener then be ready to move through the cage as fast as possible. If you are too slow you may get the gate opener killed or even get locked behind if he can't wait any longer. This often leads to a full wipe in the last room because of the extra pressure. If something goes wrong tell your party to wait unless you know they can handle it.
The second gate works exactly same as the first gate. The second cage has a pressute plate and it can be reached by taking the path on the right side. However when practising it's recommended to first kill the enemies at the second gate to reduce pressure. The second pressure plate also opens the first gate which allows your 5th player to move in. The gate opener should stand on the pressure plate until 3 players have entered the second gate and the 5th player has entered the first gate.
The last area is a cage with 2 pressure plates, 2 gates and a console. The console is locked behind a gate which opens when both plates are pressed. This also opens all previous gates which let's the 2 players get in. To open the final gate, one player has to hack the console for 10 seconds without enemies hitting him or a player stepping off his pressure plate.
The console is difficult to hack with only 3 players because a veteran dredge appears right next to the console after about 2.5 seconds of hacking. The dredge will aggro on the hacker unless he is stealthed or another player attacks him quickly. Also the players standing on plates will take lots of damage because they can't dodge and may even get knocked out of their pressure plates.
The easiest way is to use stealth. A thief can stay permanently stealthed while hacking and also give some stealth to other players. This should be done right before the second gate opens because stacking stealth is much harder when enemies are near.
If this is not possible then you should stop right after entering the second gate. You can just wait there until the 2 remaining players get to the second gate and then stand on the plates to let them in. Those 2 extra players make it much easier because they can kite the enemies. If you are kiting then take control skills to reduce pressure. Also remember to keep an eye on enemies spawning near the hacker.
Keep in mind that a common tactic is just to rush in and hope that it works out. On lower scales this will probably work fine because enemies don't deal much damage so just either go to a pressure plate or the console depending on what others are doing. If it doesn't work out then suggest something more intelligent.
The last gate opens when the hack is done. Just rush in all way to the top and kill any following enemies.
Skipping initial enemies is risky because the extra pressure may lead to a wipe in the last cage. However it's much faster so it's recommended for experienced groups. Stealth and Portal Entre makes this much smoother.
You can try killing about half of the normal enemies in the last cage if you have problems and no one can use a thief. This will reduce the pressure a lot even though they will respawn shortly.
You should have a thief on the party to trivialize the last cage. It doesn't really matter which 2 players open the first two gates as long as the thief is in the main group. Stack swiftness right when you spawn since it lasts a while and helps the gate opener to move faster.
The main group stays at the spawn and starts stacking stealth and swiftness when the gate opener is about half way. Stealth ensures that no enemies follow you through the first gate which lets you stealth again easily. Again stack stealth and swiftness when the second gate opener is about half way.
You can stack even more stealth bit after the second gate but it's not necessary. Just make sure you don't hit any enemies so you won't get revelead. The thief gets to the console and uses Shadow Refuge to hack the console safely.
You will have enemies following unless everyone managed to stay stealthed the whole time. The options are either killing them or killing yourself. If you kill them then run up and pull them behind a corner to maximize area damage. If you kill yourself then everyone expect the thief should die as soon as possible. Doing this fast requires some practice so just killing the enemies is recommended.
It's possible to jump over the first gate as long as you are out of combat (Video). Swiftness helps but is not required. This requires some practice.
Blinks can be used to teleport to the second cage from the second gate. This saves some time, especially if you have a quick way to get back. Don't use this on random parties because it probably just confuses them.
The console hacker is actually launched if a player steps off his pressure plate. This can be countered with stability or invulnerability so you can just keep hacking. This is very useful if you expect your party to mess up or if you want to do it with only 2 players.
The last cage can be done by a mesmer and a thief. The thief opens the first gate and the mesmer uses Portal Entre before the first cage and after the first gate. This allows the thief to get in too. Wait for the portal cooldown and repeat the trick for the second gate. However this time the mesmer should first take the portal to the thief so they can stack stealth safely.
At the last cage you can go directly to the pressure plates or stack more stealth in the corner. The mesmer uses Mantra of Concentration, then Blink towards the console and quickly starts hacking before it closes. At the same time the thief uses Shadow Refuge to keep them both stealthed.
If you there is a trouble with boons consider using Larcenous Strike.
Use Shadow Refuge at the console to keep you stealthed most of the time.
Use Shadow Trap when doing the second pressure plate to get instantly back.
Use portals to get everyone quickly through on the first and the second gate. Use Mimic and Portal Entre before the first cage. Use Portal Exeunt bit after the gate to let the gate opener portal through. Repeat the same trick for the second gate.
Take Blink if you need more mobility when placing portals or opening gates.
Use Spectral Walk before going to a pressure plate to quickly get out.
The start of tunnel has aand some normal-Dredge. Don't aggro them until you have killed any following enemies. Mining Suit summons normal dredge so you may get overrun unless you can focus him down or keep him disabled.
The tunnel continues to either left or right direction which depends on the fractal scale. The left tunnel is for Guns path and the right tunnel is for Bomb path.
The initial enemies can be skipped but it's not recommended without stealth because they may follow you a long way. There are also more enemies further in the tunnels so you can easily get overrun.
Once you enter the right tunnel, a group of ~4 veteran and ~4 normal enemies will rush towards you. Kill them to simplify the next part. After them there are invulnerableand turrets. Take a look at the area before rushing in.
On the right side there is a pipe which drops bombs. You need to deliver 9 bombs to the door so you can use the detonator to blow it up. However there are turrets in the way which will destroy the bomb. Stealth is the only way to avoid their shots. Use concealing dust to get stealthed. Enter and exit the dust a few times to stack over a minute stealth. If you only enter once the stealth will barely last until the end of tunnel.
Watch out for the Security Contractors. You will get revealed if you get inside their red circle which means you need to run back to the start to get stealth and another bomb. Keep in mind that a new Security Contractor appears every a bomb is delivered so the last bombs are bit harder to deliver.
Keep an eye on your stealth duration at all times. There is a concealing dust at the end of the tunnel which you can use if your stealth duration gets low when delivering a bomb. Try to keep up at least 15 seconds of stealth to avoid any surprises.
Once you have 9 bombs at the door, use the detonator nearby to blow it up. This will reveal you and spawn several dredge nearby. Run to the next room and pull them behind a corner to maximise your area damage.
Although specifically what causes it is unclear, if you spam the interact function to pick up the bombs, and then spam it again to place the bombs, you can sometimes deliver multiple bombs with just a single bomb that you are holding. In many cases, this allows you to drop of all 9 bombs.
Use pulls after using the detonator to kill enemies on spot. This is slightly faster than pulling them behind a corner.
Rabsovich appears with a dredge cart which occasionally spawns few dredge. Focus on Rabsovich while using cleave/AoE to take down other enemies. Rabsovich has 4 attacks; Shock Wave, Slice, Shield Block and Mending.
Mending is marked by a long rectangular AoE marker so you don't have to care about this animations. The attack can't be blocked so just dodge out of it.
Slice is his basic melee attack which isn't used that often. The animation is fast so there is no way to react against it. Staying at max-melee range or further prevents him from using it. However it doesn't that much damage so you can easily tank it.
Shield Block causes him to hide behind his shield which blocks all attacks and dazes attackers. You need both unblockable attacks and stability to attack him so there isn't much to do about it. Focus on other enemies until it ends.
Mending is used occasionally and it can be recognized by a weird sound. He will heal himself and summon aunless one is already alive. Disaggregator will give him regeneration and protection making him even more tankier. The heal can be interrupted, sometimes even through defiance bar.
If you have trouble you can try pulling Rabsovich away from the dredge cart.
Way to the final boss
The dredge cart will blow up against the door whendies. This will reveal a tunnel to the last boss. The tunnel is filled with either dredge or ice elementsl which depends on which way you took earlier. If you went to the left path with guns then you will see dredge. Otherwie you will see ice elementals.
The last boss will be same type as the enemies here. You will faceif you see dredge and if you see ice elementals. All enemies are veterans so skipping them is recommended.
Run or stealth past the enemies. After the tunnel turn left immediately so you won't aggro the final boss until the party is ready. Keep going until enemies stop following you.
The Final Boss
The basic idea is the same for both bosses. They both have an extreme amount of health so just killing them would take a very long time. There 4 huge lava buckets in the room, one each corner. There is a lever on top of a bug which causes it drop some lava below. The lava does nothing to players but inflicts Superheated-debuff on the boss which causes it take 10x damage.
Decide who handles the lever pulling. That player should use ranged weapons so he can also deal some distance when possible. Keep in mind that it's possible that the boss aggroes on the player pulling levers so be ready to improvise if needed. Other players must kite the boss to the correct spot. Break his defiance once you hear the sound of lever being pulled. This ensure he will stay on the spot and gives you a nice burst.
Lava buckets have a cooldown so you need to keep moving to the next bucket to keep the superheated debuff up. Both bosses have a powerful self healing which also removes all conditions. The ability won't work as long as the boss has the debuff.
The common tactic is to start with the nearest bucket and move in the clockwise direction. However there are other variations with practically no diffence so take a look at what others are doing. Splitting up and doing your own thing will just get everyone killed.
You should pull the boss to the next bucket as soon as possible no matter what tactic you choose. This leaves you about 15 seconds until the debuff expires. The lava should only be dropped when the debuff is about to end because it doesn't stack. If the lever puller drops it way too early then notify him about it. The fight will last about twice as long if you need to constantly move around.
Some parties may first attack the boss on spot and pull him bit later. This also works but it's more suspectible to errors.
It's important to keep using the lava buckets even if someone gets defeated. The boss will very likely aggro on you if you start resurrecting immediately. This will mess up the rotation and the boss will probably get to full health. Instead pull the boss to the next spot as you would normally do. Then go out of combat and resurrect if the boss isn't following you.
Make sure you stand between the boss and the next spot at all times so he gets pulled to the right direction. Try to stay near the boss to increase your chances to get aggro. If you get aggro then other players can deal melee damage more easily.
Consider taking a ranged weapon which you use when pulling the boss to the next spot. It's possible to also melee him but you will get aggro very easily because of the close distance. When the boss is aggroed on you he isn't moving towards the next spot and you risk the debuff running out. Feel free to use melee weapons when the boss is on the next spot.
Rotate between 2 lava buckets. Their cooldowns are short enough to keep the debuff up almost all the time. This allows you to benefit from static buffs like banners and spirits more often.
The lever puller should jump down after pulling a lever to deal melee damage while the defiance is broken.
Ice Elemental is easier then thanbecause his attacks are well telegraphed and easily avoidabled. Ice Elemental has 4 attacks; Shatterstone, Polar Smash, Freeze Row and Mending.
Shatterstone is used when he jumps. The attack causes an ice shard appear over every nearby target. After ~2 seconds the ice shards drops dealing area damage, launch and agony. You can simply move out of these but don't hesitate to dodge if you are surrounded by these. Getting hit by multiple shards will probably get you downed.
Polar Smash is used when he pulls his right arm behind his back. When he hits the ground a big ticking PBAoE will appear which deals lots of damage, chilled and agony over 3 seconds. It's important to dodge away from him. Moving out is also an option if you saw the animation early. The attack will instantly kill targets without proper agony resist.
Freeze Row is used when he waves his arms and causes a distinct sound. He will create a lots of small delayed AoEs in a V-shape. They explode after 2.75 seconds so you have plenty of time to move out. Each explosion deals damage and launches. You may take lots of damage if you get hit multiple times.
Mending is used when he kneels down. This is the powerful healing ability which also removes conditions. It will get interrupted by normal attacks as long as he has the superheated debuff. The attack also summons 3which can't be prevented. Use area attacks to kill them while focusing Rampaging Ice Elemental. Stay mobile to avoid their slow attacks.
All his attacks can be easily avoided by just moving away from him. Remember to not pull him too far from the lava bucket spot.
Melee can be difficult because of his high powered close range attacks. It's important to recognized his animations so you can dodge on time. Polar Smash causes some down time since you need to wait until the PBAoE ends.