The Flame Leviathan fight comprises of 3 different vehicle types thats are all utilised in different ways to help defeat the boss.
Siege Engine - effectively the tanking vehicle
Driver
Button 1 -
Ram - It deals 25,000 damage to any targets in front of the tank (melee range only) and knocks them back.
Button 2 -
Electroshock - This ability must be used by Siege Tank drivers to interrupt Flame Leviathan's Flame Vents ability.
Button 3 -
Steam Rush - During the boss fight use this ability as an escape mechanism to help kite Flame Leviathan.
Most important role on the boss:Kite when targeted and use steamrush if the boss is too close. Interupt Flame Vents with Electroshock
Gunner
Button 1 -
Anti-Air - Deals 15,000 damage to any targets within 10 yards. Takes out floating Pyrite Satellites so that Demolishers can refuel during the fight.
Button 2 -
Fire Cannon - This deals 50,000 damage to any enemy hit by the cannon blast
Button 4 -
Shield Generator - 1 minute cooldown. Absorbs 100,000 damage for up to 5 seconds. It is used as a defensive ability during the boss fight.
Most important role on the boss:DPS boss and use Shield if boss gets too close during kiting
Demolisher - the dps vehicle
Driver
Button 1 -
Hurl Boulder - Deals 30,000 damage to any targets within 8 yards of the boulder's impact point.
Button 2 -
Hurl Pyrite Barrel - Deal 60,000 damage on impact and applying a stacking DoT effect that deals 12,000 damage. It stacks up to 10 times.
Button 3 -
Ram - This knocks back all enemies in front of the Demolisher, dealing 20,000 damage.
Button 6 -
Launch Passenger - Mechanics on the Demolisher can load themselves into the main cannon. Demolisher driver can fire the mechanic player onto the back of Flame Leviathan.
Most important role on the boss:Kite when targeted. Stack pyrite to 10 stacks onto the boss for huge damage. Launch passenger (gunner) when required.
Gunner / Thrown person
Button 1 -
Mortar - Deals 11,000 damage to any targets hit by the blast. It also ignites any tar laid by choppers.
Button 2 -
Anti-Air - Deals 15,000 damage in a 5 yard radius. It is used to knock down flying Pyrite Satellites for retrieval.
Button 3 -
Grab Crate - Grabs a targeted available pyrite canister, which reloads the pyrite/energy bar of the Demolisher's main driver by 25 units.
Button 4 -
Increased Speed - It is used to help kite Flame Leviathan or escape danger on hard mode.
Button 6 -
Load Into Catapult - The mechanic loads himself into the Demolisher's main cannon, allowing him to be launched onto the back of Flame Leviathan.
Most important role on the boss:Shooting down Pyrite and grabbing it to reload supplies. Load yourself into the catapult for the driver to fire you onto the boss and then dps the 4 turrets asap.
Chopper - fires oil to slow and damage the boss and rescues players

Button 1 -
Speed Boost - This doubles the speed of the bike for 5 seconds and costs 50 energy.
Button 2 -
Sonic Horn - This deals 7,000 damage to enemies in a 35 yard long frontal cone in front of the bike.
Button 3 -
Tar - Drops a pool of tar that slows enemies who move through it. Tar can be ignited by Demolisher mechanics or Siege Tank gunners. If ignited, enemies moving through the tar take 6,000 damage per second.
Button 5 -
First Aid Kit - This heals the Chopper passenger to full life over 4 seconds. It is used after picking up a player from Flame Leviathan's back.
Most important role on the boss:Fire tar into the kiting path of the boss so it slows him down. Pick up and heal demo gunners after they have been thrown at the boss.