#56 - Greninja in Smash Bros

Greninja was chosen as a playable character in Smash Bros 3DS/Wii U even before Pokémon X/Y were revealed. All reference material Sakurai had to put Greninja in the game were sketches, and he had to stay up very late only to capture Greninja's animations.

SOURCE: http://www.siliconera.com/2014/06/10/super-smash-bros-characters-decided-upon-early-development/