Dr. Lugae is a storyline boss in Final Fantasy IV. It is the fiend form of Doctor Lugae. After the battle, Dr. Lugae's Key will be obtained for use in the Tower of Babil to stop the cannons from destroying the dwarves.
Dr. Lugae will use Reverse Gas inflicting the Reverse status that can only be removed at the end of the fight, or if Dr. Lugae uses Reverse Gas again. The Reverse status causes damage and healing to have the opposite effect on the party and Dr. Lugae. He uses it as his first action of the battle and will continue to use it along with his other attacks.
While the party members are under the Reverse status, Dr. Lugae will use restore on them to damage them doing around 600–800 damage. When they are not under Reverse he will use Flamethrower to do similar damage, although a character with Ice Shield or Ice Mail won't take as much damage. Dr. Lugae counters any magic cast on him with a Sleeping Gas attack.
There are two ways to tackle the Dr. Lugae. The easy way is to use two Elixirs on him when he uses Reversal Gas on his first move. Although wasteful, it's very effective. The other is to keep an eye on the Reverse status and not attack with any characters while having Rydia heal the party with Black Magic and have Yang charge up Focus up to three times while equipping the Lightning Claws until Reverse is removed. To recover HP while under the Reverse status, the player can make use of the attackers in the party to attack each other and gain HP. After Dr. Lugae removes the Reverse status with Reverse Gas, Rosa should heal while the others attack.
Another way is to summon Whyt when Rydia is in Reverse status, which will remove it. If Rydia is brought back when the others are in Reverse, she will not be. This means that Rydia's status is a reverse of the other party members'. Ergo, Lugae will use Restore when Rydia isn't in Reverse status, healing her, and will use Flamethrower when Rydia is in Reverse status, also healing. Rydia is effectively unable to take damage from Lugae's attacks.