- Hoppin' Jack, King Slime, and the Spiked Slimes he spawns are not affected by the Royal Gel.
- Flying Slimers and Gastropods, though they are technically not slimes, are affected by the Royal Gel.
The item seems to be useless to more advanced players, but it can be used as surefire protection during a Slime Rain. It also lets you ignore more powerful Hardmode slimes such as the Slimer if you are not well enough equipped for those enemies. This item is also useful if you are going into The Underworld on expert mode due to the Lava Slimes or facing the Gastropods in the Hallow (Since they can pick off players even when off-screen).
- Added to the game.