If you specifically need Build 12112017 for mod compatibility or speedrunning purposes, you can often "downpatch" the game if you own it on Steam:
: You can use the Steam console to download specific older "depots" of the game using SteamDB identifiers. Download Rain World Build 12112017 ONLINE
: Occasionally, developers leave older stable builds in the "Betas" tab under the game's properties in your Steam Library. If you specifically need Build 12112017 for mod
It is highly recommended to download the game through official digital storefronts. These platforms ensure you receive the most stable, secure, and up-to-date version of the game, including support for the Downpour DLC and community mods. and up-to-date version of the game
: The primary platform for the game, offering full Steam Workshop integration for easy modding.