This guide assumes that you already have at least a basic knowledge of C#, and have set up a modding environment as explained on this wiki.

A custom Game Mode is essentially a completely unrestricted challenge editor mode that is present in the GUI as a button alongside the vanilla game modes like Deflation, Apopalypse or Half-Cash.

ModGameMode

Required Overrides

BaseGameMode: A common pattern among modded types, this is the game mode to use as a starting point that you can edit from. Best to get the value from the Mod Helper provided GameModeType class, or GameModeType.None to start off empty.

Difficulty: Which difficulty menu the button should be a part of, one of DifficultyType.Easy, DifficultyType.Medium or DifficultyType.Hard.

ModifyBaseGameModeModel(ModModel): Add the custom rules to your Game Mode here. This will mostly come from adding/changing its MutatorModModels, or using extension methods to do that.

Common Overrides

DisplayName: What your Game Mode should be called in the UI

Add an Icon (512x512) for your Game Mode to use in the round changer by using including a .png with the same name as your class, or using the Icon / IconReference properties.

Tips

• Internally, the word "Mod" is used to describe Game Modes, which is why the type you edit is a ModModel

• Use the Mod Helper's extension methods for modifying the ModModel

Example

This is a Game Mode to go alongside a custom All Regrow round set. It has a base of GameModeType.None because the properties of Medium difficulty apply by default unless manually overriden.

public class AllRegrowMode : ModGameMode
{
    public override string Difficulty => DifficultyType.Medium;

    public override string BaseGameMode => GameModeType.None;
        
    public override string DisplayName => "All Regrow";

    public override string Icon => VanillaSprites.RegrowBloonIcon;

    public override void ModifyBaseGameModeModel(ModModel gameModeModel)
    {
        gameModeModel.UseRoundSet<AllRegrow>();
    }
}

A modified version of Deflation for Hard difficulty using the values from BTD5

public class OldDeflation : ModGameMode
{
    public override string Difficulty => DifficultyType.Hard;
        
    public override string BaseGameMode => GameModeType.Deflation;
        
    public override void ModifyBaseGameModeModel(ModModel gameModeModel)
    {
        gameModeModel.SetStartingCash(50000);
        gameModeModel.SetStartingRound(30);
        gameModeModel.SetEndingRound(80);
    }
}