The best modding information

The greatest resource for modding is of course, the wiki. For me though it did have an outdated bit.

Setting up your project

You’ll have to set your project up under Other .NET, And Library. The Wiki was outdated and didn’t have good screenshots for this.

xnb files

You should get familiar with the various XNB files that make modding the game very easy.
dialog
schedule
General NPC Data

Adding a new character

I would only use a mod like this on new saves. I have had some issues, with removing the mod afterword, and then the savegame is no good. I think this can be remedied but have not looked into it. Here is the ModEntry.cs file:

using System;
using System.Collections.Generic;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using StardewModdingAPI;
using StardewModdingAPI.Events;
using StardewValley;


namespace Mary
{
    public class ModEntry : Mod, IAssetEditor, IAssetLoader
    {
        private IModHelper modHelper;
        public override void Entry(IModHelper helper)
        {
            modHelper = helper;

            helper.Events.GameLoop.GameLaunched += this.OnGameLaunched;
        }

        public bool CanEdit<T>(IAssetInfo asset)
        {
            // Prepering to edit files.
            if (asset.AssetNameEquals("Data/NPCDispositions"))
                return true;

            if (asset.AssetNameEquals("Data/NPCGiftTastes"))
                return true;

            if (asset.AssetNameEquals("Characters/Dialogue/rainy"))
                return true;

            if(asset.AssetNameEquals("Characters/Dialogue/rainy"))
                return true;

            return false;
        }

        public void Edit<T>(IAssetData asset)
        {
            // Editing existing game files.
            if (asset.AssetNameEquals("Data/NPCDispositions"))
            {
                asset.AsDictionary<string, string>().Data["Mary"] = "adult/shy/outgoing/positive/female/datable/null/Town/fall 9//Tent 2 3/Mary";
            }

            if (asset.AssetNameEquals("Data/NPCGiftTastes"))
            {
                IDictionary<string, string> NPCGiftTastes = asset.AsDictionary<string, string>().Data;
                NPCGiftTastes["Mary"] = "Now that is a lovely gift, @. It will really help me!/227 228 220 428 440" +
                    " 787 247/That's so nice of you, @!/724 725" +
                    " 726 303 350/Uh... I'm not sure what should I do with this./2 24 90 174 190 336" +
                    " 194/Why would you even give this to me?/149 205 281 404 420 422/Thank you.//";
            }

            if (asset.AssetNameEquals("Characters/Dialogue/rainy"))
            {
                IDictionary<string, string> rainy = asset.AsDictionary<string, string>().Data;
                rainy["Mary"] = "I hate it when it rains.$s";
            }
        }

        public bool CanLoad<T>(IAssetInfo asset)
        {
            //Preparing to load the assets.
            if (asset.AssetNameEquals("Characters/Dialogue/Mary"))
            {
                return true;
            }

            if (asset.AssetNameEquals("Characters/Mary"))
            {
                return true;
            }

            if (asset.AssetNameEquals("Portraits/Mary"))
            {
                return true;
            }


            if (asset.AssetNameEquals("Characters/schedules/Mary"))
            {
                return true;
            }


            return false;
        }

        public T Load<T>(IAssetInfo asset)
        {
         

            if (asset.AssetNameEquals("Characters/Dialogue/Mary"))
            {
                return Helper.Content.Load<T>("assets/Mary_dialogue.xnb", ContentSource.ModFolder);
            }

            if (asset.AssetNameEquals("Characters/schedules/Mary"))
            {
                return Helper.Content.Load<T>("assets/Mary_schedule.xnb", ContentSource.ModFolder);
            }

            if (asset.AssetNameEquals("Characters/Mary"))
            {
                return Helper.Content.Load<T>("assets/texture.png", ContentSource.ModFolder);
            }

            if (asset.AssetNameEquals("Portraits/Mary"))
            {
                return Helper.Content.Load<T>("assets/portrait.png", ContentSource.ModFolder);
            }


            throw new InvalidOperationException($"Unexpected asset '{asset.AssetName}'.");
        }




        private void OnGameLaunched(object sender, GameLaunchedEventArgs e)
        {


            Monitor.Log($"Mary Mod Loading");

        }


    }
}

As you can see in the code I did have to create a schedule file and a dialogue file, which I created by unpacking a different characters xnbfiles, using xnbcli. The xnbfiles of varying types can be found where ever your steam library is: SteamLibrary/steamapps/common/Stardew Valley/Contents/Resources/Content/. It’s very easy to add filesm as you can see in the Load function. Sometimes your files won’t load for various reasons, it’s going to be a little trial and error, I had some issues with the schedule ones. Just keep fiddling.

Currently Unemployed

As I am currently unemployed perhaps you would want to click my amazon affiliate link and buy a C# Book on Game Programming