You can find the Grimrail Depot dungeon entrance within Gorgrond, Draenor.
The coordinates are (55.2, 32.1)
1. Borka the Brute & Railmaster Rocketspark
/i Kill bosses close together as one gets more powerful when other dies. Move out of red circles on ground. Railmaster jumps on the boxes, tank now position Borka at boxes so his Mad Dash will knock down Railmaster.
Heroic Differences: Borka uses Slam damaging all in front of him, avoid this.
2. Nitrogg Thundertower
/i Nuke boss in room until he retreats. Run to the front of train (wind pushes you back). Take cover behind crates to avoid Suppressive Fire. Dps loot adds (Shrapnel & Grenades use on adds, Mortar Shells use on boss). When his cannon destroyed nuke boss.
Heroic Differences: Move away from Slag Blast, the blue flames the boss fires at certain locations.
3. Skylord Tovra
/i Run out of blue lightning patches on the ground. Avoid standing on freeze traps. Tank should face boss towards outside of the train to help protect party from Spinning Spear.
Heroic Differences: Throws an explosive spear at a targets location causing fire damage when it lands. This puts a Hunter’s Mark above the targets head, move away from others.