Nice Concept,
but it was obvious at one or two points in the animation that you had gotten lazy, (The 'Shadow rushes into a bunch of clones' scene, for instance.) and the concept was sort of... Loose? Super Mario Bros. Z already has Sonic and Mario with a DBZ fight style, and Naruto? Why? Little to NOTHING was known about the story, and I'm sure that others would want more if say, and cliffhanger was added. (This ending doesn't count in my opinion.) For all we know, Sonic and Naruto are going to a video game party and want Shadow to join them. Also, if you're using sprites for the animation, it may be a good idea to use pixel art for the background, the two seem to clash at almost every point in the movie. If you can, swap one of the two art styles, either start drawing Sonic, or start pixelating backgrounds. Overall, I think it was a good effort for your second flash, and I look forward to watching the second one.
Verdict-
Visuals: 4/10
The visuals were alright to say the most, and the two art styles need to work co-operatively.
Sound: 6/10
The sound effects are overused in almost every flash that involves fighting, but I can take them.
Concept: 3/10
We need to learn more about the story, and it needs to be less like Super Mario Bros. Z
Animation: 5/10
It was alright, but you need to not be lazy, and put your FULL effort into the flash.
Overall: 5/10
As a final comment, I ask that in your next flash that you spell check/Use better English, if you can. It wasn't so bad that I couldn't understand, but it was an annoyance.
I can tell you'll work your way up from this, and I'd love to see you grow amongst the ranks, I'll be back reviewing part 2, when and if it releases! Good luck!