Minecraft as Roblox: Roblox avatars, items and UI on a baseplate, with Roblox's real oof.
Minecraft: Java Edition, but it's Roblox: a Roblox baseplate, Roblox avatars, Roblox items and a Roblox-style UI.
Avatars: every player is a blocky Roblox character (classic noob, red shirt, purple, black & white) wearing Roblox's real face.
Items: you start with a Roblox backpack: the Jump Button (speed and jump boost), Robux (right-click to heal) and Reset Character (oof, back to spawn). Their icons are Roblox's own.
UI: Roblox's font, a green Roblox health bar, a dark rounded hotbar and buttons. Hunger is gone, just like Roblox.
Map: spawn on the white pad in the middle of a huge gray baseplate. Climb the colorful obby, avoid the red kill bricks, and don't fall off the edge: you'll hear Roblox's real oof and respawn.
What's from Roblox: the sounds, sun and moon, face, font, health-bar color and item icons are read from your own Roblox install when the game starts. Nothing from Roblox is shipped with this mashup.
How to play: press Play. The first time, a Prism Launcher window asks you to sign in with the Microsoft account that owns Minecraft: Java Edition; after that it launches straight into the Roblox world.
You need: Minecraft: Java Edition and Roblox installed. Single player.
Credits: Prism Launcher (GPL-3.0, PrismLauncher contributors) and Fabric Loader / Fabric API (Apache-2.0, FabricMC) are bundled. Mod code CC0.