Although I have met all of the requirements, I still cannot fight Regice.
---I have originally owned + quest enabled + off my team: Dugtrio, Crobat, Golem, Ariados, Weavile, Hitmonlee, Hitmonchan, and Hitmontop.
---I have the Ice Fruit.
Any help appreciated, thanks.
The Pokemon also need to be off your gallery and trade. If all else fails, double check that all the Pokemon are enabled for quest and originally owned (especially the Golem) and that you have the ice fruit in your bag. As far as I know, the quest functions fine, just need to have everything.