There are 4 towers associated with Flame Leviathan and each one adds something new to the fight in addition to increasing Flame's health. Each tower gives him 50% more health! You must speak to Lore Keeper of Norgannon in order to have the option to keep towers. This achievement is the fourth level or tier of the hard-mode associated with Flame Leviathan. Below are the abilities associated with the towers:

• Tower of Storms - Will allow Flame to use Thorim's Hammer and give him the Tower of Storms buff of 25% extra physical damage.
• Tower of Flames - Will allow Flame to use Mimiron's Inferno and give him the Tower of Flames buff of 50% increase in Fire damage. The Inferno spell is an AOE that leaves a circle of fire on the ground. Try to avoid these as much as possible as they do a lot of damage!
• Tower of Frost - Will allow Flame to use Hodir's Fury and give him the Tower of Frost buff that slows players speed by 20%. Hodir's Fury will cause Frost damage and if you stand in the beam long enough, it will encase your vehicle in a tomb of frost. The tomb causes A LOT of damage and can be removed by igniting the Chopper's Tar underneath the target.
• Tower of Nature - Will allow Flame to use Freya's Ward and give him the Tower of Life buff that will reduce Fire damage taken from Flame by 10%. Freya's Ward will summon Writhing Lasher and Ward of Life adds.

As you can see by the list of abilities, that it will take quite a bit of coordination and probably a lot of wiping before you get this achievement. It's not an easy achievement to get, but also not impossible. Work up to it one tower at a time!