Spawn Conditions

Queen Slime can be spawned in the Hallow by using a Gelatin Crystal—if used outside the Hallow, nothing will happen and the item will not be consumed. The crystal is consumed upon use, immediately summoning the boss.
The Gelatin Crystal can be found in the Underground Hallow among Crystal Shards growing on Pearlstone and Pink Ice blocks.

Stratigies
In her first phase, Queen Slime jumps around in a similar fashion to King Slime, though much faster. She periodically summons Crystal Slimes, Heavenly Slimes, or Bouncy Slimes. Crystal Slimes will shoot several crystals upwards, Heavenly Slimes will fly towards the player, and Bouncy Slimes will fire bouncing shots towards the player. After a few jumps, she does one of two things, chosen at random:
• Will stay in one place for a few seconds, before jumping very quickly towards the player and attempt to stomp them, dealing high damage.
• Will stay in one place for a few seconds, before firing 6 Regal Gel that bounce twice before breaking. Sometimes, she will perform this attack multiple times in a row.
Killing the smaller slimes should be a priority during this phase, as they can quickly overwhelm the player.
When at 50% health, Queen Slime will grow wings and begin to fly like a Slimer. Her AI also changes:
• She will occasionally shoot Regal Gel in 10 directions.
• She will occasionally attempt to fly above and drop down onto the player.