Architect is a Hollow Knight level editor mod allowing you to add platforms, enemies and more to change areas in the game.
You can make these changes with the in-game editor, and can share them with your friends in multiplayer using HKMP.
Architect has a wide range of objects to place down and configuration settings to use, allowing for lots of creativity!
Using the Collaboration Mode you can also work with others in multiplayer to edit things together, and you can share them with others online using the in-game level sharing system, as well as browse the levels other people have uploaded!
You can find the full guide for Architect here.
