I spent way too much of my free time in Maelstrom today, and I learned the boss mechanics well enough to write a veteran guide. I only reached the final boss of arena 8, and I have not done it on normal yet either so I can't explain arena 9 at all anyway.
Achievement progress for all 9 arenas on veteran
i.imgur.com/i0U4l6m.jpg
Twitch replay of me going through the arenas if you want visual representations (this includes me experimenting and learning the mechanics, it's long)
twitch.tv/fat_cat45/v/19418204Arena 1
This will be the most simple of all the 9 arenas. The only environmental factor is a floating orb that follows you. Simply keep moving forward and you'll be fine.
The boss: 1 enemy which spawns adds. Just focus the adds first then go back to the boss. There's really nothing special here, a standard fight.
Arena 2
One of my favorite of the arenas. A dwarven arena with rotating blade traps as seen in Skyrim. There are 3 layers to the traps, and they overlap with one another. Think of it as 3 circles, one larger than the next. The inner circle rotates counter clockwise, the middle circle rotates clockwise, and the outer circle rotates counter clockwise.
The strategy to this is to move along the outer ring, counter clockwise, and follow that blade. Then once the blade catches up behind you, walk into the middle circle to let the outer circle blade pass you and then go back to the outer circle and continue to follow it.
The boss: 3 different dwarven centurions. You have to damage each one enough to "shut it down". They shut down about every 25% hp. The "shut down" lasts for about 20 seconds, or until no other dwarven centurions are not standing, then one of the three will stand up. Keep following the rotation of the blades counter clockwise and focus each centurion as they become available. Make sure to do it 1 by 1 to minimize how many are active at once.
Arena 3
A swamp with 4 land masses like corners to a square. The environmental effect here is that from time to time the swamp water will become electric and zap you for about 14k damage a tick. One thing to watch out for is the Stranglers that spawn in the water. Whenever you see one spawn, kill it first before all else. A lot of my deaths occurred from being pulled into electric water.
The boss: A standard Lamia with lots of life. Just play it safe, kill stranglers, kite the boss, and kill adds before boss. Playing smart for this boss fight is the easiest way to complete it.
Arena 4
Another dwarven ring. The environmental effect here is that Dwarven Sentries will spawn on the outside of the arena, then move to the center around a pillar. If there Sentries are allowed to channel next to the pillar for 5 seconds, they become immune and shoot lightning at you. These Sentries are extremely weak with only about 15k life. Although, if the sentries do become active around the pillar, it is possible to move to the other side and completely avoid any damage by using line of sight.
The boss: Think of vet darkshade final boss. A dwarven spider with multiple phases. It's basically a replica of the lightning phase and fire phase from vet darkshade. Not much else to it. Just hide behind the pillar when it is lightning phase, and deal the damage during fire phase while avoiding the fireballs falling from above.
Arena 5
A frozen lake with 3 ice platforms. The environmental effect is that the ice will kill you over time, exactly the same as veteran Dragonstar arena 2 with the blizzard. Trolls will spawn in the exact center of the lake and then move to one of the 3 ice platforms at random. If these trolls are allowed to channel for 6 seconds, the platform will be destroyed. They can be interrupted with a bash, but not stuns. They are fairly weak, about 35k hp.
This arena is extremely biased toward mobility and ranged DPS. If your character is solely melee, well, you'll have a terrible time here.
The boss: A female giant who uses the same moveset as normals giants. A conal cleave, a fear, and a standard smash attack. However, at 70% and 35% the boss will destroy an ice platform. IF a troll destroys a platform during the fight you WILL die. The only way to succeed is to prioritize any troll that spawns and keep all 3 ice platforms up at once.
Arena 6
A spider daedra room with a bunch of eggs. This is by far my least favorite arena, so be warned. There are 5 totems, 4 corners and 1 in the center. A horde of small 150k hp spider will spawns from time to time, and the only way to get rid of them is by standing next to one of the totems while they are "glowing gold". However, these totems will be covered by spider webs which are placed by an enemy called "Webspinner". The only way to remove the webs off of the totems is to kill a roaming Hoarver on top of the totem, or throw the acid sack from its corpse on top of the totem. The acid dissolves the web and the totems becomes available again.
This is by far the most complicated environmental effect, and the most deadly. The totems turn on and off at random, and unless you keep 2 or 3 totems open at all times, you may get hit by a spider horde and none of the totems are glowing gold to get rid of them.
The boss: A giant spider daedra who doesn't have any special attacks. This boss does have an enrage mechanic, and the only way to avoid that enrage mechanic is to have all 5 totems cleared of webs at the same time. This will reset the boss's enrage timer as well as stun her for 10 seconds. This may sound simple, but it is extremely difficult. You have to make sure any totem isn't getting undone by a Webspinner, pull Hoarvers on top of webbed totems, move to golden totems when spider hordes arrive, dodge the lightning from spider daedra, kill the adds, and then kill the boss. God damn, I hate this round with a passion.
Arena 7
A venemous room with plants growing inside. If you step on top of these plants, they have an AoE that expands which will then explode. This explosion, if you are caught in it, will do roughly 8k per second for 20 seconds. There are pools of green liquid southwest and northeast, walking into these pools will purge the poision DoT. It is also possible to use any ability which purges to get rid of that poision DoT. During the mobs there will be summoners which spawn on the stone platforms. These summoners rapidly increase the spawn rate of the plants as well as make them all explode after spawning (so that stepping on them isn't the only way to trigger them). Focus them first every time.
The boss: A huge Argonian Behemoth. Do not let this boss get melee range to you, there are 2 lethal attacks. One is a bite which does around 25k, and one is a bleed which does 5k per second for 8 seconds. The bleed can be purged. Besides those 2 melee attacks, there is a 3rd mechanic which will usually result in an instant death. The boss will channel and glow red. If you do not interrupt that channel, the boss lets out a scream and you will die (it does over 50k). IF the lightning mages are alive they will place a protective shield upon themselves which you may also stand in (think of the boss guarding the drawbridge lever from Arx Corinium, the snake and lamia). Sitting in these shields lets you DPS the boss for free instead of interrupting him with a bash, I advise you take advantage of these bubbles.
Arena 8
Not much special here besides fireballs shooting out of lava, and the 3 binding stones. During the normal waves one enemy in specific will spawn, and that enemy will have a blue aura around them. The only way to damage that enemy is to destroy the binding stones. Usually for the normal waves only 1 of the 3 stones activate and need to be destroyed. The mobs are pretty straight forward, some daedra and some fire atronachs.
The boss: This boss is insane. This is where my journey ended in veteran after about 50 lives on it. Like before, the boss is immune to all damage when the Binding Stones are active. Except unlike the previous rounds, all 3 stones become active instead of 1. Adds will spawn about once every 15 seconds, and these totems have about 60k life. ALL 3 totems must be destroyed before you can damage the boss at all. Once all 3 totems are destroyed, you can damage the boss ONLY FOR 7 SECONDS. Then all 3 totems will reactivate and adds will continue to spawn again. Each add has about 100k life, except flame atros at 40k. This boss fight is the epitome of high burst damage with a lot of sustain. The lowest I ever got this boss to was 30%, and it took 20 minutes to reach that point.
My thoughts
Maelstrom Arena is awesome, but some of the mechanics are reliant upon randomness and not too fun to play. It is such a good challenge, and the mechanics were fun to learn and manipulate (such as using Purge from Alliance War skills, or Ball of Lightning for mobility around the arena). Unless you are a hardcore PvE player, you will not have fun on veteran mode. You will die, you will die a lot.
Also...
On PTS, my skills and abilities on deal about half damage of what they should on live client.