Before Installing this mod, be sure to install BOTH Mod The Gungeon and Kyle's Custom Characters Mod. Both are needed to run the mod.
First, download the mod by pressing the download button. From there, you need to bring it to the "CustomCharacterData" folder in your ETG directory, typically found at "C:\Program Files (x86)\Steam\steamapps\common\Enter the Gungeon".
From there, extract the character folder from the ZIP file and place it back into the same "CustomCharacterData" folder. If the ZIP file is still there, delete it.
Launch the game. You should be able to find the character to the right of where all the main gungeoneers are.