Steam Train

The Steam Train is a Hardmode Boss and considered to be the final one of the Steam Trio bosses.

Spawn
The Steam Train, like most other bosses, does not spawn on its own and requires the player to summon it with the Suspicious Train Whistle.

Behavior
The Steam Train will attack by moving across the screen in a horizontal pattern, shooting steam and projectiles into the air to deal additional damage.

Phase 1

 * The Steam Train will send steam and cogs into the battle and can move in a horizontal pattern.
 * Fires multiple emissions of steam, sending down Gas Balls on tiles.
 * Fires another steam attack that can home in onto you.
 * It fires one Coginator, which will follow you, dealing additional damage.

Phase 2 - Superdrive Mode

 * The Steam Train travels faster and fires projectiles more often.
 * Firing 4 homing Coginators.

Phase 3 - Hyperdrive Mode

 * Steam Train travels even faster and also starts firing homing steam blasts.

Phase 4 - Warp-Drive Mode

 * Heal half of the health by 15% roughly.
 * Steam Train once again travels even faster than before.

In Expert Mode

 * Gains ability to inflict Steamy debuff.
 * Boss’ speed now increased further.

Aftermath

 * Once defeated, the Conductor will be able to arrive if provided suitable housing.

Tips

 * The Steam Train can be fast though, as the boss moves across the screen, going horizontally from the left to the right and vice versa. Using the map will help, displaying the boss' location.
 * Both weapons Chlorophyte Shotbow and Steamstring are an excellent choice for playing Ranger. The former shoots three arrows with Holy Arrows and can even shoot at a distance, making it a good choice while the latter shoots two brass arrows instead of three, also a good choice, but keep in mind that the arrows that are shot are extremely fast.
 * The Cupid's Bow can be considered useful as each of mysticism can be a great choice for a perfect battle:
 * Destruction Mode can turn Cupid's Bow into a boomerang which is capable of throwing an infinite amount of boomerangs at once.
 * Illusion Mode can turn it into a bow, which inflicts Lovestruck on normal enemies but does not inflict the debuff on Bosses so it's useless.
 * Conujuration Mode can summon cupids but only two can remain, which shoot different projectiles that will work when they disappear for a few more seconds.
 * While the Steam Train appears to have many segments, it is really a single, very long sprite (shown below).

Trivia

 * Unlike other steam bosses, it does not have a steampunk version of any vanilla bosses itself.