I’m currently searching for a way to play coop with an AoE2 AI against another player. At the moment, you can currently use the “debug” mode in single player to play a somewhat restricted coop with an AI against another AI. I’m not sure if you can do this with a custom map or scenario. I tried a little myself, but I did not find a working way. I guess you need to go deeper to do this. If anyone has an idea or is working on something similar, please let me know.
The underlying idea is to use the AI as assistance for multitasking or doing stuff you don’t want to do in the game. This is obviously not meant for competitive play and more meant as his own game mode. A year ago, I made a video about it and used the “debug” mode to demonstrate the basic concept. I added the link to the video just for extra context about what I have in mind.