Damn, that Triclyde knocked me out of my chair. The running Mega Man was pretty sweet too. Well done all!
How to make them:
Search google for sprites or use the NES Sprite Database (again, google it), save the images and then blow them up 500% in some kind of image program (Photoshop, Paint Shop Pro etc). Slap a grid on there (CTRL+G or something like that...) and you should have a one-for-one representation. If you choose well and have the required colors, it shouldn't take more than an hour to put one together. Smaller ones like Kirby take even less time.
As for Alucard not being that big... I dunno, he kinda has to be, right? I mean, all these NES ones are one-for-one, pixel-for-block big. Someone like Alucard or maybe Ryu would have to be much larger. Or am I just not getting it? Either way, that's a ton of blocks and yeah, a lot of colors. Most of which probably don't exist in PixelBlocks.