I was just going to write an awesome fangirling comment but when I realized you were accepting critique, I just had to do it.
The colors , EVERY color you used in this picture balance out perfectly. I love how the umbrella from her drink landed in her hair in the midst of the frisbee mishap XD Did I get that right?
And how Pinkie is just plum terrified.
This piece is nothing short of a humorous masterpiece! There's really nothing I can offer you as far as constructive critique, as the simple style in itself (with the clear amount of effort put into the linework alone) does this picture just enough justice, everything about it is just spot on.
I love how you outlined every thing to look like a cartoon, and the shadowing is cute, and modern. You have a great technique, and style. I love how you have Celestia do her mane. It looks so fashionable! Its like she's a teenager again. And Luna's face is so priceless. It looks like she's about to burst from laughter! Also, Pinkie Pie is hillarious! She seems to think that Celestia is going to send her to the moon! Lastly I would like to say I love all the small details you put in,like the spiled drink. It means alot in the art.