Pretty good
It was a funny idea, but it feels like it's definitely already been done. How the heroes are preparing to fight, and while they are, the threat already finishes and leaves. Yeah, I can't put my finger on where exactly, but I've seen it somewhere else.
The animation and sound effects were good, but I wasn't fond of the lack of detail in the background and lack of color in just about everything.
You never name Captain Fantastic in the animation. Granted, it's fairly easy to infer his name based on the CF on his uniform and the fact he's leader of the Fantastisquad, but mentioning it even just once for the sake of clarity would be nice.
When they're all standing together, side by side, Gun Man's gun looks a bit crooked.
And I'm not very fond of Roman Five, considering he's just a mash-up of memes.
All around decent. Nothing amazing, but not a waste of time either.