So what is Marshmallow Duel? If you've never heard of it before, it could best be explained as a Super Smash Bros. type game, but from an earlier era and stranger minds.
Marshmallow Duel DS is a complete rewrite and evolution of the original Marshmallow Duel, designed for the Nintendo DS console. It is a 2 player deathmatch game of luck and skill where each player tries to knock their opponent into the deadly marshmallow pit or destroy them with one of the 18 weapons that randomly spawn in the map.
If you don't have a Nintendo DS, you can still run it on an ordinary PC via the use of a DS emulator. I have put some info here on just how to do that. Information related to running on DS hardware can similarly be found here.
The current version, v2, features the following:
Marshmallow Duel DS is free open-source software, released under the GNU General Public License.