Greninja's ability Protean:- Explained Differently<
Greninja becomes the type it used last according to it's moveset last used, also takes on weaknesses and strengths along with it.
Greninja With Protean fires ice beam and becomes an Ice type and thus has weaknesses to all ice type weaknesses! BUT If a Pokemon like Volcarona with 4x speed outspeeded Greninja with Giga Drain with it's water type still in effect it would be KO.
Volcarona with 3x sp.atk/ 3x sp.def / 3x speed vs Greninja
252+ SpA Volcarona Giga Drain vs. 0 HP / 0 SpD Greninja: 404-476 (141.7 - 167%) -- guaranteed OHKO
Greninja has good points and bad. It's ability can be useful or the death of it!