My friend's OC, Dirtfang, as a playable character in Enter the Gungeon. You will need mod the gungeon and the custom characters mod to install this.
Custom Characters Mod: https://modworkshop.net/mod/24802
Mod the Gungeon: https://modthegungeon.eu/#download

How to Install:

• Install mod the gungeon
• Run the game, this will create a mods folder (close the game after)
• Put the Custom Characters Mod into the mods folder
• Run the game again, this will create a custom characters folder (again, close the game after)
• Unzip the dirtfang folder into the custom characters folder
  For more detailed instructions, read the instructions on the Custom Characters Mod