In the first stage of the fight, Duke Moltron will launch explosive balls of lava at the player while chasing them around. These have 60 attack power and inflict the 'Scorching' debuff. Moltron himself has 100 attack power in this stage, and inflicts 'Scorching' as well.
The second stage is unlocked when Duke Moltron hits 30000 . His attack power increases to 130 in this stage, and the lava bubbles will stop. He will start to spawn Magmatic Fish to chase the player in this stage, and gains a ray-type attack. The ray attack will be shot from his eyes as a solid beam. Moltron will spin completely around in this attack, forcing the player to either run ahead of the beam or hide behind something to protect them. The beam has 150 power and inflicts the 'On Fire!' debuff. Moltron will also start summoning lavaspouts from the surrounding lava to shoot up at the player. If the player is struck, they will take damage as normal and be shot into the air.
The third stage is unlocked when Duke Moltron falls to 5000 . It is informally called the "death throw"stage. Duke Moltron will become incredibly fast and get 180 attack power. Boulders will begin falling from the ceiling of the Underworld, dealing 70-160 damage upon contact. The lava ray attack will persist, but instead of spinning around once, Moltron will spin around 3 times when executing it.
Upon death, Duke Moltron will explode with a power similar to Dynamite, dealing heavy damage and probably killing any player in the blast radius. His drops will be left in a circle of Demonite Bricks so as to not have them destroyed by lava. All Magmatic Fish in the area will die.
Killing Duke Moltron will unleash the War Mode Underworld.
Only one of the following will be dropped
Credit for the summoning and original idea of this boss goes to SlayerOfTheBad.