Dark Legend

Unfortunately, unlike you, who was interested in doing Nuzlocke challenge in Xenoverse, I was interested in doing Pokedex challenge from the beginning.

I only did pass 1(since that was the only one out when I last played) but Hell Greninja was a goddang nightmare. The usaual status-abuse for X pokemon didn't work and it's hard withstanding its offensive power. I honestly forgot how I beat it.

But Mega Legendary Beasts from Pass 2 are even stronger than X Greninja. And not to mention, a powerful opponent from Pass 3.