The purchase of the full game includes the functionality for friends to download a Wi-fi multiplayer battle edition of the game for free.
Dr. Mario's Virus Buster, a WiiWare launch title in Japan and presumably a WiiWare launch title in other regions once the service launches worldwide later this year, has a special feature up its sleeve.
Owners of the full version of the game have the ability to send a message to anyone on their Wii friends list which will enable them to download a free demo version of the Dr. Mario WiiWare game. The demo version allows players to play classic Dr. Mario multiplayer matches against friends only, provided Dr. Mario game friend codes have been exchanged. There is no single player mode or any way to play the game offline in the demo.
This video takes you through the process involved with downloading and setting up the free Dr. Mario WiiWare demo.
This demo feature makes it possible for people who have not downloaded Dr. Mario to try the game out before buying it. However, it is not possible to send the demo to American or European Wii consoles, so you can forget about asking your friend with a Japanese Wii to send you the demo unless you've got a Japanese Wii yourself.
Perhaps more importantly, this confirms that WiiWare is capable of supporting free demo games. As more games are added to WiiWare, we'll see if there are more free demos of this sort or if games with demos will appear from companies other than Nintendo.