A basic starter for a Rimworld Mod using Harmony

HarmonyMainTemplate.cs

using Harmony;
using System;
using System.Linq;
using System.Reflection;
using Verse;

namespace Namespace
{
	[StaticConstructorOnStartup]
	static class YourMod
	{
		static YourMod()
		{
			var harmony = HarmonyInstance.Create("com.whatever.is.your.modname");
			harmony.PatchAll(Assembly.GetExecutingAssembly());
		}

		// start rimworld with -rungame "savegamename" to activate this
		[HarmonyPatch(typeof(UIRoot_Entry), "Init", new Type[0])]
		static class UIRoot_Entry_Init_Patch
		{
			static bool firstTime = true;
			static void Postfix()
			{
				Environment.GetCommandLineArgs().Aggregate((prev, saveGameName) =>
				{
					if (firstTime && GenScene.InEntryScene && prev.ToLower() == "-rungame")
					{
						PreLoadUtility.CheckVersionAndLoad(GenFilePaths.FilePathForSavedGame(saveGameName), ScribeMetaHeaderUtility.ScribeHeaderMode.Map, () =>
						{
							firstTime = false;
							LongEventHandler.QueueLongEvent(delegate
							{
								Current.Game = new Game() { InitData = new GameInitData() { gameToLoad = saveGameName } };
							}, "Play", "LoadingLongEvent", true, null);
						});
					}
					return saveGameName;
				});
			}
		}
	}
}