Queen Slime

The Queen Slime is a Hardmode Hallow-themed boss summoned with the Gelatin Crystal. It's appearance is that of a massive pinkish-violet slime wearing a tiara with what seems to be an enlarged, more crystalized version of a Gelatin Crystal inside it.

Spawning
Queen Slime can be spawned by using a Gelatin Crystal. This can be done in the Hallow at any time.

Gelatin Crystal can be found in Underground Hallowed mixed with Crystal Shards.

The Gelatin Crystals appear to change color from pink to blue.

Trivia

 * She appears to be the Hardmode counterpart to King Slime.
 * Queen Slime’s AI was created entirely by developer Grox the Great, while the visual effect was created by Yoraiz0r.
 * The Queen Slime is one of 5 bosses with exclusive music, the others being the Empress of Light, Plantera, Duke Fishron and Moon Lord.