Marshadow, Tapu Koko, Alola Raichu, Mimikyu, Aegislash, Non-Mega Rain Abusers (namely Kingdra & Ludicolo).
A less common threats would be Landorus-T (w/ Flyium-Z).
Besides Alola Raichu, every threat mentioned above can use a Z-Move, but are also perfectly viable without it, thus adding a new...