It wasn't a dream. There really is a video game coming that crosses the world of Pokémon with that of Nobunaga's Ambition, a Japanese history series developed by Tecmo Koei. This is its trailer.
See? Not dreaming. That's a trailer.
The game's full name is Pokémon + Nobunaga's Ambition, and it's out on the DS next year. If you think it's coming out in the West, then yes, that part, you're dreaming.