With a few people, we made a codebase as well as a modified engine in C++ to work with KH III.
This was definitely a monstrous task, but the base allowed people to create:

• Levels
• Skeletal Rigs
• Static Meshes
• Animation Graphs
• NPCs
• Flash specific UI

This was done for a competition that Tiny Build was hosting.
The goal was to make a mod for Hello Neighbor in Unreal Engine a month before release, and what I created featured:

• A new area
• 6 unique levels
• Cutscenes
• Minigames/Puzzles
• Light story elements

A Minecraft mod that I made a long time ago.
The mod was programmed in Java and was one of the first mods I created.
It featured:

• A new dimension/biome
• Custom Mobs
• New Items