Pokémon + Nobunaga's Ambition is the strangest crossover this side of Kingdom Hearts. Not only does it mix a historically-inspired series with a monster-catching one, it also mixes a team-centric strategy game with a one-versus-one traditional RPG. And how does this odd combination work out? Pretty well, actually.
As you can see in the game's first boss battle above, Pokémon + Nobunaga's Ambition utilizes the elemental strength/weakness system from Pokémon not only in regard to attacks, but in regard to the terrain as well. And with up to 5 other trainers on your side, the tactical gameplay is well preserved.
Pokémon + Nobunaga's Ambition was released in Japan on March 17, 2012. As of the date of this posting, there have been no announcements concerning a Western release.