Antisocial Alison
Antisocial Alison is an iMessage sticker pack available in the iOS App Store. This repository contains the Xcode project of the sticker pack, which can be used as an example for other sticker packs. The project can be opened with Xcode 9, and contains only one target, a StickerPackExtension.
Development
Pngyu is a good application for reducing PNG file size to meet the 512 KB limit per sticker.