iOS 11.3 was a minor update to the iOS emoji set. The main change in this release is the modification of four emojis used in Apple's separate Animoji feature. First announced in January 2018, this release was finalized in March 2018.
Apple emojis are displayed on iPhone, iPad, Mac, Apple Watch and Apple TV as part of the Apple Color Emoji font. iOS, macOS, watchOS and tvOS all display the same emoji set from Apple. iPhone X models also support interactive Animoji and Memoji features.
The following two Private Use Area characters are not cross-platform compatible but do work on Apple devices: