Royal Gel

Royal Gel is an accessory obtained from the Treasure Bag dropped by King Slime in Expert mode. While equipped, Slimes become passive and function similarly to Critters, although they cannot be captured. They will no longer pursue the player, deal damage on contact or fire projectiles, even if the player deals damage to them first. This applies to all slimes, excluding Hoppin' Jacks, Queen Slime and her Bouncy Slimes, Crystal Slimes, and Heavenly Slimes; and King Slime and his Spiked Slimes, though the normal Blue Slimes that King Slime spawns remain docile. Minions and NPCs will continue to attack nearby slimes.

Trivia

 * Royal Gel's name may be inspired by "Royal Jelly", a food substance that bee workers feed to bee larvae to change how they grow, specifically so the larvae can become a queen bee.

History
Gel Royal 皇家凝胶