Keldeo, Princess Peach and her castle are respectively from Nintendo's Pokemon and Mario and this screenshot's taken from Valve's Garry's Mod. It is done through Forestvoid24's choice as a celebration of Pokemon Day.

For some reason, Keldeo found a P-Balloon and inflated her belly silly. She seems to enjoy it that it makes her as happy as a flower. Meanwhile, Peach looked very shocked to see a Pokemon blowing up huge like that and wonders how this balloon get there in the first place.