Greninja has some interesting combo possibilities, but often isn’t commented on; be it that the Pokémon is high mid tier in Super Smash Bros. for Wii U, it’s likely that it is not seen as viable as other characters in the competitive landscape.
However, this tutorial is hoping to break that perception. Greninja has some interesting properties on its Up Air, which not only has an up-reaching but also a down-reaching hitbox, each with their own uses. While the upward hitbox can be used to extend combos, the downward hitbox can be used to bounce opponents off the ground, leading to even more combo potential as a starter move.
Source: HASC Poga