You're in charge of implementing fusions, or fusion evolutions, or fusiolutions, or whatever into the next big main series Pokemon game.

You can't just say "lol this is stupid fuk fusions". Your assignment came down from the project manager, so you won't have a job for long if you don't cooperate.

How do you implement fusions so that they're competitively balanced and easy to use? How do you go about introducing the concept to the player?