Vibrant Reverie/Ardorix

Ardorix is a Pre-Hardmode Boss, spawned with Fiery Egg. It's a fiery Phoenix that resides in The Underworld, able to withstand huge amount of damage and revive stronger than before.

Spawn
It can only be spawned with Fiery Egg, which can be crafted or rarely dropped by Fire Imps. It can be only be used in The Underworld.

Behavior
Ardorix is a flying enemy, flying over the player. Normally, it fires 3 flames in a spreaded arc, with the center directed to the player. It then rams the targeted player for a while and then returns to fire flames.

Dealing too much damage in a short time will make it become ethereal, becoming invincible for a short while. It then reappear and can be damaged again. After becoming vulnerable again, Ardorix remains stationary to charge it's powerful flamethrower, which is then unleashed like a bullet hell pattern. The attack follows (very slowly) the player if it dodges. To prevent this, players must stop deal damage to Ardorix for a while, encouraging short-burst damage. However, you can freely damage Ardorix while it's charging and using the flamethrower. After a while, it returns normal.

In Expert Mode, Ardorix can withstand more damage before becoming ethereal. This is to compensate the health increase, and increases with more players that join the fight.

Trivia

 * This boss refers to the Firax from the Reborn Mod.
 * Furthermore, the boss was originally named Phoenix from said mod.