Canterlot is under attack and the Mane 6 have been granted the knowledge and ability to fend off these surprise invaders by an unknown magical benefactor.
I don't think I've ever tried to fit this many characters into one pic before, and I'd say my first try isn't half bad. Through to be fair this is based on one of the inspirations for this idea, that being the changeling attack on Canterlot. Only instead of shape shifting bugs it's ninjas now: the Ku-neigh-ichi (I feel like I should be more ashamed of that pun than I am).

This is a clan of warriors for higher who make their livings by working as spies and thieves, but their coffers have been running low so they decided to attack Canterlot to boost their reputation and get ahold of a lot of valuables. They aren't dumb though, they make sure to stack the deck in their favor: the royal princesses are away on a diplomatic trip, most of the guards have been rendered unconscious with sleep gas pumped into their barracks during the night, and most of the residents of Canterlot have been scared away with smoke from controlled flames and the bangs of loud (but not harmful) explosives. They'll take enough to make a good sized pile of bits and be gone without a trace before the day is out with minimal damage to the city (why invite more retaliation than needed).

How well do you think their plan will hold up with the Mane 6 on the job? We'll just have to see. More Siege of Canterlot on the way.
I don't own these characters just the pic.