Some dude is making a whole show about a Mario and Sonic crossover and it's pretty good. The graphics are mostly sprites, but at times there are 3D GC graphics or other misc graphics. The plot is good and thick with lots of surprises and twists. Every episode is full of characters and new and interesting settings and events. The battles are creatively orchestrated and a joy to watch (like the Super Mario vs. Dragon Ball Z battle videos that I posted many months ago).
The only downside is that dialogue is written which kinda slows the faced paced flow of the show. But on the other hand that stop-dialogue kind of gives you a feeling that it's a game, not a show so it might not be a bad thing. Especially with lots of Paper Mario and other Mario RPG sprites, the whole thing looks really well done.
I won't spoil you anything, but rest assured that this is quite a good waste of time. There are currently 8 episodes of variable length (all together at least 3 hours) and the 9th episode is in progress (the first part has been done). I also recognized two memes and while the first one was funny to see, but still a bit expected since it's a Dragon Ball Z styled show (power level over 9000), the second one was perfectly placed and I didn't see it coming at all (do a barrel roll).
http://www.youtube.com/watch?v=s1kzRQl6o-0&list=PL79B9CAF84ACFDC1DI wish there were more episodes and the show was already done. I hate to stop watching a show in the middle. Worst thing, the end of episode 8 is a really nasty cliffhanger.
In any case, enjoy it. Oh, BTW, it starts to get really interesting at episode 3. You can actually skip the first two episodes, but I still recommend you watch them as they are entertaining enough.