Alrighty, this is my first ever critique, so bare with me!
First off, I love the way you did the emotions. You can really see the determined, yet fierce and angry gaze in the leaping dog, who I'm assuming is Blu. Lucky looks really shocked and horrified as he stares at the unknown enemy. I also love the shadowing and it really looks like the end of an alley way.
Now, I hope this isn't too harsh, but here goes. The main thing I see here is anatomy. Overall Blu's face looks good, but I would suggest making his body a bit longer to match the size of the head. His right, hind leg looks way too long and the left hind leg seems too short and tucked in. I would maybe try have one or both of the legs sticking out behind him. Now his front legs and paws look too big and could maybe be smaller and thinner. Overall, looks good! ^-^
Now the only main problem I see with Lucky is his hind leg. The haunch or thigh I should say looks too small and not positioned right. I would also suggest, for the back wall it just looks a bit too scribbly. xD
I hope this wasn't too harsh but I like it a lot and I hope this helps!