Loved it as much as all the others, but...
I feel it could have been better.
1) "O rly?" Come on. I don't care if the Koopa Bros. are SUPPOSED to act lame, O rly is dead. Thinking about the Ginyu Force and how lame they are, I suppose lame characters are all right--as long as the other characters react to that like they feel dumber for having watched it, otherwise I'd just assume it's crappy dialogue.
Remember Frieza's reaction when he saw the Ginyu force strike their poses for the first time? Remember how -everybody- reacted to Saiyaman? Stuff like that.
2) The jokes weren't as good as they were in the last three. Luigi-is-a-pussy jokes are way overdone. Sure he's a coward, but come on, a fly could land on his nose and he'd hit the deck shivering at this rate.
3) The Spirit Squad thing was kickass. Excellent work there.
4) It irritated me how long Peach's eyes were popping when the Emerald got snatched. I mean, yeah, ZOMG THE EMERALDZ IS GONE but that was a little unnecessary. Felt like something you missed when it went through the editing process.
5) Speaking of the chaos emerald, I feel it would have been better to do the Zoom In >>> "I GOTZ ME AN EMERALD" Jingle -after- their "OMGWTF" reaction. Doing it before their reaction felt diminished its impact, and to me, stuck out like a can of peaches in between the mattresses when trying to sleep.
6) "Enter the Koopa Bros" was a poor choice for a title. I hate it when the characters know less than I do about the plot and I haven't even finished the thing yet--unless it creates suspense, and in this case, it completely removed all traces of it. We knew it would be the Koopa Bros who stole their emerald, both because turning out the lights and not killing anyone doesn't seem Mecha Sonic's style (if that was the only clue it would have been great), and mainly, because you told us so when we pressed Play. As a result, we end up waiting for their introduction. Waiting sucks.
If they had been a surprise, I'm sure a LOT of people, including me, would have said "Holy crap, it's THEM? I completely forgot they existed!"
"A New Threat" was a better title, comparing it to this one, because it gave nothing away, and it gave us the sense that there was something dangerous lurking ahead, creating suspense. (It was also quite a bit of a surprise that Yoshi was the one to fight. Good job with Episode 3).
Don't take my critique the wrong way at all, I love what you've done with the series. I just wish people would critique the fan fiction I write like this instead of just giving it a 10/10 and going "ZOMG THAT ROCKZORED MAKE MORE!" :/ How are you supposed to get better if you don't know what to improve upon? I hope you continue to make the rest of the episodes as thrilling as the first four have been. If at least one of your episodes doesn't make top 50 by the end of its third week, there is no justice, just people who rate 0 because it has DBZ associated with it.