This dungeon has some trash to be concerned about, so Ill go over them a little before the bosses.

Trash leading up to the first boss isnt too crazy, but there are some goblin adds (I think they were engineers) that should be focused down.  They will run to iron stars in the room, once reaching them they will try to activate it.  Interrupt or stun them.  If an iron star goes active, it will roll into a wall a deal group wide dmg.  The bigger adds just charge a random player.

First boss encounter Rocketspark and Borka isnt anything too crazy.  Rocketspark just jumps around the room and fires missles at players.  One ability will target 2(normal) or all players(heroic) with reticles.  Move as soon as they appear, they hurt.  He will jump up on boxes for a channeled barrage attack.  This is where Borka come into play.  For the most part Borka is underwhelming.  Just keep him in the middle of the room.  Shortly after Rocketspark jumps up for his channeled ability have the tank face Borka towards him.  Borka will charge and stun Rocketspark, interrupting his channel.  Just rinse and repeat.  On heroic Borka does a slam that deals grp dmg and interrupts spellcasting for 5 secs.  Dont be casting when this goes off.

Trash to the second boss isnt too terrible, but should utilize CC's to make it easier.  Their are several types of orc adds.  Grenadiers, Boomers, and Gunners.  The ones you need to be concerned about the most are the Gunners.  You need to face them away from the group, they will spam cast a flame ability that deals a lot of dmg.  There is one pull in particular where there are 2 of them, the definitely need to be CC'd.  If they both are positioned wrong and cast into the group then GG, death.  Good thing to remember (which I had a hard time doing) was that once they start casting, you can strafe out of it.  So tanks just make sure to keep strafing left or right while they are spam casting it so you dont spin it into the group.  The grenadiers and boomers arent too severe.  They just throw grenades and bombs into the group.  There is another mob, named cinder-something, that will toss fire patches on the ground, just move out of those.

Second boss, and everyones favorite, Nitogg Thundertower, is the bastard of the place.  He is also the "turret boss".  You dps him for a while inside the room, then he will open up the train and retreat to his turret, constantly firing at you and focusing on a player.  When he focuses on a player, just have them LoS behind a pillar to avoid his barrage.  He will constantly spawn adds into the fight.  Infantry (just cleave down), Grenadiers, and Boomers.  On heroic he will also spawn the Gunners, do your best to face them from the group.  But thankfully on heroic they just dont sit there and spam cast at you, so you CAN reposition them a bit to help out.  During this fight you objective is to stay line of sight of the boss as much as possible.  Deal with adds then click on their bodies to obtain their "weapons".  Grenadiers drop grenades that you can use via your extra action button.  You should use these to help kill all of the adds quickly.  If there are no adds up, use them on the boss.  The Boomers give you shells which will allow you to use the turrets on the sides of the train (you can see Saedo using them in the vid), you will use the turrets to deal the most damage to the boss' turret.  You can also use one of the abilities on the turret to help kill adds if you dont have any grenades.  Once the boss' turret is destroyed he jumps out and you just kill him the rest of the way.  In the vid you will notice fire covering a significant part of the train and we have to retreat backwards, it deals a lot of dmg and leaves a nasty debuff.  That is only on heroic, there is no ground fire on normal.  Also, if you have a shaman, or another caster with a significttn knockback, you CAN knock the adds off the sides of the train to watch them go bye-bye, but by doing that you risk losing grenades or shells to use on the boss.  So utilize that wisely.

Trash up to the last boss isnt bad, just wait for fire to be gone on either side of the one car, then run as fast as you can past it so you dont die.  Then the last cars trash can be pulled in small packs.  Nothing really special about them.  Once you kill the last pack, go back to the entrance of that car so the boss doesnt land on you.

Last boss Skylord Tovra isnt too terrible.  Her wyvern will do fly bys and drop lightning patches in the ground that despawn after a while.  She will also throw a "spinning spear" at random players.  This is similar to the gunners that once she begins her cast of it, you can side-step and avoid the dmg.  She will also throw traps randomly at players, these can be dodged if you move quick enough, otherwise you get frozen in place and can take a bit of dmg.  On heroic she places a hunters mark on a random player and will throw an explosive spear at the target and deals dmg to anyone with 8 yards.  Also the lightning breath lasts longer and will eventually fill up the floor, sort of a soft enrage.  It will still despawn as it did for us, but you will unavoidably have a full platform for a while if the fight lingers too long.