CoS Boss

CRADLE OF SHADOWS 1st BOSS (Sithera)

Sithera is more like a "miniboss", larger version of monster that appears all over dungeon. Before fight, its good to light up all 3 braziers. Boss will be turning them off one after another with her HP loss. You cant relight same brazier again so you have to move during fight and kite boss with you so she stays in light. After fight clear trash and continue throught dark corridors.

CRADLE OF SHADOWS 2nd BOSS (Khephidaen)

This boss follows very strict pattern of attack. Hardcoded pattern running like a clock. Also, dark/light mechanic applies.
Attack pattern is frontal cleave attack (DD+HEALER dont stand in front of boss) then some random attacks after that she will cast a large aoe growing from under her feet from with EVERYONE including tank have to run away (otherwise its 1 hit KO). After that she will teleport into random place and start casting random attack that will hit every member of group. This attack should be interrupted but if not it can be blocked. After that she will do another single target cast that can be interrupted too. And here she wil go back to beginning.
The aim for tank here is to taunt and kite boss into the light. Tank has to notice where the boss is, run to closest light possible and then taunt and kite here into that light. You want to minimise distance that boss has to walk through shadow to the light (because while she is shadow your damage is poop). What is going to INTERRUPT kiting boss is her channelled attacks. When she is casting she stops moving. This is where DD come in. They both should have some kind of ranged interrupt to stop boss casting ASAP (so she can be kited into light faster). Its also good if when she is casting, one of DD will approach her from behind and try to bash her into the light (if she is very close).
The fight is extremely fast paced, last time i was counting, boss attack rotation takes 15-20 seconds to finish, this means every that 15 seconds she will teleport to random place and will have to be lured into light again. Each time not interrupted cast is wasted time (because her internal rotation clock is still ticking during that).
At fixed health % she will turn off some of the lights. With each light turned off an shadow add will spawn there that will be summoning trash spiders (they have like 12k hp on vet). Lighting up brazier again will prevent add spawns.
The health % when last lights go off is around 20%. A good strategy is to stop dps before that, somewhere around 22%, then stay within light and stop chasing boss, optionally interrupting her ranged attacks with range interrupt (venom arror, crushing shock) and wait for her to teleport somewhere centrally in the light you are in and as soon as she ports to you and she is in light nuke her before she manages to turn off last light (that is if you go for the "no re-light" achievement)
Pros Tip: most of times when she teleport she will be standing very close to the edge, when interrupting her attack try to do it so she gets pushed into the light, not outside of the light. You can interrupt her attack the turns of the lights so you don't have to deal with shades and trash spiders.

CRADLE OF SHADOWS 3rd Boss (Votary)

Quite easy really. Boss uses standard spider mechanics like feeding of dead bodies (bash him), beside that she will poison one of players and that player will start spawning poison AOE where he stands, he should move away from group. Boss also has large AOE growing from boss location that has to be avoided at all cost (1 hit KO).

CRADLE OF SHADOWS 4th BOSS (Dranos Valedor)

This is an interesting, fun and dynamic fight. I like it the most of all dungeons. During fight, a Mephala shrine will throw bombs all over room (tank can eat up damage, DDs try to stay away or block). Boss will do a random attack similar to one that final boss of Spindleclutch does. The attack will hit each player once in a random sequence. When you see him attacking first player, everyone should simply block. Those attacks also leave AOE rune fields that will disappear after short time. This boss can also cause up to 50K damage, so hope to get a Tank with a boat load of HP to work around this and eat up the damage. So make sure they are fully healed before the boss finishes charging the attack.
During fight boss will split into orange spirits. At this point he will gain damage shield that nullifies any damage (cant be burned). Goal here is for DDs to destroy orange ghosts and collect "essences" they drop. At this time tank should try to kite boss into other orange ghost because it will cause boss and ghost to merge. When all ghosts are dead/essences (orange balls dropped by ghosts) collected damage shield will disappear
After damage shield phase boss will be likely to summon two adds that will beam/chain one person (usually tank) they have to be interrupted and killed, if not its 1 shot KO for beamed person (Vet Fungal Grotto flashback)
At around 30% HP shrine of Mephala will start spiting damaging waves. Play mechanics at this point and try to stand away from the centre of room.
Extra achievement in here is to not absorb any orange essences during shield phase. You do it simply by having tank kite boss to each of orange adds so boss can suck them in (where normally you have DDs split to kill adds and pick up essences).

CRADLE OF SHADOWS 5th FINAL BOSS ("Lady of Lace")

This is the most annoying boss in whole game in my opinion. So much RNG and so much things that can mess you up.
Adds. They will be spawning during fight and have to be killed ASAP because you dont want even more AOE and damage in there.
Ulti feeding. Boss will pick one player at random and drain his ulti. Its advisable to use ultis at will to not let it be wasted. Its currently debatable whether it can be interrupted or not (i believe its not possible to interrupt).
Bubbles, BUBBLES Every. AND YOU EVEN MORE BUBBLES! EVERYONE GETS BUBBLES! Red, Blue and Green bubbles will roam around room after ulti drain phase. Red will damage you, Blue will drain magicka, Green will drain Stamina. Whoever the boss sucks in and violates for a few moments...the bubbles will depend on whatever pool highest for that player: Magicka, stamina, health and possible Ultimate.
Other noticeable boss attacks in here is frontal cone AOE that will follow tank (like Crematorial Guard) so DD and Heals should stay at the back or sides of boss. Boss will be applying DOT on tank that hits hard so keep heals up on him (and tank should also have way to self heal). I heard that this DOT can be dodged if you do it fast after boss finishes her cone attack. Also you don't want to stand any AOE. There will be those very dark black AOE on the ground that will melt you very fast if you try to ignore them.
Shadow sense, boss will use her shadowsense to hunt you down with her spikes. The most annoying mechanic of all.

At one point of fight boss will retreat to centre of room and climb up to celling and your screen will turn dark (like slow-mo, adds in room will also kind of slow down). When you see this happening STOP MOVING. Seriously, stop moving and stand still. You can heal, you can put on shield, you can use skills that wont move you an inch and you can res people that are nearby but you have to stand still. A green tiny aoe circle will appear under your feet. You have to stay still inside it.

It will take some time, like 2-4 seconds of standing still (it feels weird, i know) but then your screen will turn normal and what you should be looking for is the moment that tiny green circle that was under your feet fades out. THIS IS THE MOMENT. You have to dodger roll once and then immediately dodge roll again. If you do it successfully you will see that you avoided a central spike attack and then AOE that is around spike.

Pay attention to group-mates, don't roll/don't walk into them because your spike will kill them (vet Crypt of hearts pre final boss flashback).

The second way to do it is more mag users friendly since it requires just one roll or sprint. You stand still, then your screens returns to normal and green circle disappears from under your feets this is where you start walking. Not sprting, not rolling, just walking. After taking 2-3 steps you will see a ground rumble below your feet, clouds of dust, this is when you roll. One dodge roll should get you out of spike AOE that will come up exactly where you noticed the ground rumble/dust cloud.

Banished to catacombs mechanic. During a fight 2 flesh atros will spawn. Kill them asap and have healer or tank pick the light (X synergy). If tank and healer are new in dungeon, someone who done it before should take it. Somewhere at 65% and then again around 30's boss will banish you to catacombs. At this time you want to make sure you have 2 people with light of atro (it will be very large yellow AOE coming from each players with that synergy).

Catacombs are kind of a mini maze that is shaped like a hourglass with boss room in the center point. Players will be divided into groups of two. One group in top other in bottom. Goal is to come back to boss room and stay alive.

Things that you will encounter in maze: hoarvors that will zerg you if you stay too long in one place, nightblade daedras that will stun you and snare you, spike trap pads that will snare and damage you, savage argonian that will help you killing one of daedra adds.

Now why did you need atro light for? The light/dark rule applies here and atro light... well lights up your path and will also reveal on which trap pads you can stand and which to avoid (they will be red).

Its generally advised to let the tank + dps team come out first, boss hits like a truck... Also it WILL happen that healer team will be late so EVERY member should have some self heals. Vigor for stamina, offbar resto for magicka with ward etc.

Things helpful in maze: rapids to remove snares and move faster, anything that can stun enemies like dragonknight's claws, caltrops, mines. Self heals are necessary for group that does not have healer. Also its good if the person that carries the light wont abandon other group member behind lol (it happens so often when light carriers is stam based and can CC break all the time and sprint while person behind is magicka squishy light armor).

Unconfirmed but my friend kept raging about it. He would say: hoarvors gain speed each time you attack them or they will catch up with you and touch you. Trying to snare them, throw caltrops or attack them would lead to wipe. Same goes for turning around and running close to them (and being attacked). I personally did not notice anything like that.

I also noticed during the Don't Move Phase, you can successfully avoid the spike aoe if you roll out as soon as you see a dirt cloud under your feet. Saves you from having to use up stamina rolling more than once.