Hi first time posting on here and am a novice at developing. Okay so my buddy and I were reminiscing on or childhood and ended up playing a game of Yu-Gi-Oh. He had all the good cards (literally everything) So we were able to use these crazy stacked decks and it was pretty fun. Anyways what I wanted to do is make a Yu-Gi-Oh game with all the cards that exist where I can play my friend online. We both have android phones so that helps. Anyways how hard would it be to develop the game. I don't want to put it on the store or anything like that. I just want it so we can play each other whenever. The official online Yu-Gi-Oh game for android is kinda what I want but it is riddled with micro transactions for cards <_<. I just want to develop the game so we can build a deck of any cards we want to choose from and play online against my friend. I have no idea how to do this but I want to learn. Please anyone point me in the right direction.

Yu-Gi-Oh, the cards, the specific rules, and the rest are owned and protected by all kinds of IP laws. Don't use any of it.

You might consider starting with the Generic Collectible Card Game engine or something similar. It already does most of the work.

Even if I dont advise to use it, you could simply build and setup android apps in Unity3D. There might be some card game assets at the asset store for now, otherwise there would be some steps to do like making an asset for each card including a full body material, scripts to define rulings and at least a controller that is able to call events on that scripts like OnDrawn, OnPlaying, OnPlayed, OnTurnedFaceUp, OnAttack and OnDestroy.

Cards then need to exist logically in some kind of list for each player and need an instance from the asset when drawm/ put on the table. I did something like this a time ago and it is work anyway to bring up something from scratch

Take a look at HTML5 and ThreeJS. making a web version of this would probably be the easiest way. All mobile platforms now support native webview apps. They are Apps that are coded to run in a web-browser but have access to a devices's native API. making the game itself wouldnt be that hard, but you would have to create the infrastructure, all the server-side code to make it multiplayer.

As was stated before. using the Yu-Gi-Oh! IP, would get you sued. but their is no harm in making it just for yourself and a few friends

The official online Yu-Gi-Oh game for android is kinda what I want but it is riddled with micro transactions for cards <_<.

This is typical of app stores and mobile devices. Perhaps you can get hold of a similar Yu-Gi-Oh game for Gameboy/DS, Playstation etc?