Remember all those "mystery toy" lines in the 90s, where you'd buy unknown capsules that would sometimes dissolve in water? Many toy manufactures are still making them actually, preying on our child-like sense of curiosity -- now, Nintendo seems to be in on the fun. Starting today, Club Nintendo members can now grab "Surprise Me Boxes" for 300 coins apiece. It looks like they're already sold out, but keep the page bookmarked in case they restock.
Nintendo claims that the box has at least 500 coins in rewards, so you have a good chance of salvaging something eBay-able in the haul. The real downside is that they don't actually ship in a question mark box, according to the website -- it'll come via standard mail packaging (which is lame, considering they already made a ton of boxes for the 2010 Platinum reward -- I'd totally pay more for an authentic box). Whatever mystery you decide to uncover, don't forget that Club Nintendo's digital offerings change soon for May!
Mario's Surprise Me Box [Club Nintendo]