Many years ago I played a silly game "Clash of Clans"-type game (it was a knockoff). The game itself wasn't super fun (build things, wait for them to finish or pay to speed up, PvP, clans, etc) but I played it for a few months on and off. Randomly one day I decided to hook up a network proxy to the game and look at what data the game sent/received.

It turned out that when you queried the map it returned a ton more data than it displayed (data you would normally need to scout for). Also a ton of endpoints, like the one to load your own town's info, would also work if you used an enemy's town id (but with your auth key still). There was little to no verification/authentication blocks that I ran into.

I spent the next 2-3 weeks writing little CLI tools to talk to the API cultivating in a small suite of web-based tools that used assets I ripped from the game to display info (using the currency icons, using the building sprites, etc) until I got bored of the game and the reverse engineering and just walked away. It was fun for a little bit operating with perfect knowledge and using some of that info to put my thumb on the scales for myself and my clan but in the end it become more work than fun and so I stopped.