The Clockwork Dragon, also known as Mech Dragon, MachDragon, Mech D., or D.Machin, is an enemy from Final Fantasy IV.
It is a particularly evasive and rare monster when attempting to complete the Bestiary in the GBA and subsequent versions (a Siren used in the Giant's Stomach will spawn one in the PSP version, but two MecGiants in the SNES version). It appears only on the floor before the final floor as well as on the Giant of Babil's Inner Stair (the same place one fights the Elemental Archfiends). The long, bridge-like area it appears in and its low encounter rate is a reference to Warmech from Final Fantasy.
With a devastating melee attack, high hit points, and an extremely powerful, party-affecting fire attack, the Clockwork Dragon is likely to be the player's first real taste of the "end of game" dragons, such as the more powerful Blue and Red Dragons, which will appear in the Lunar Subterrane.
As Clockwork Dragon can inflict a lot of damage quickly, it is advised to take advantage of Fusoya's ready access to spells like Thundaga, Meteor and Flare to wear down its HP. Rydia should use Bahamut and Ramuh for much the same reason.
An easy way to vanquish it is to simply have Rydia or Fusoya cast Stop on it, allowing Cecil and Edge to easily wear down its HP.
Also, Clockwork Dragon is vulnerable to Tornado, reducing its HP to single digit area and pretty much any attack will kill it afterwards. If timed correctly, the Clockwork Dragon won't even get a turn before it gets disposed of.
Special care should be taken in the 3D release, as the Clockwork Dragon deals considerably more damage and has more HP (which is true of a great many enemies in this remake). The party should use Slow to reduce its speed, but it is otherwise a similar battle to the other releases, damage and HP aside.