LostMagic gave me the best handheld multiplayer experience I've ever had!
IMO, the multiplayer duels typically consist of two halves(if the two mages are anywhere near equal matches). The first half typically consists of a Starcraft-style RTS showdown between your battallion of about 9 to 11 monsters, and you're opponent's own battalion, usually consisting of an equal number of monsters. During which time it's also a good idea to use your magic to assist your monsters somewhat, by either sending homing fireballs or stone pillars, or mana dragons into the battlefield, or by using special magic spells to increase your own monsters' stats, or to even lower your enemy monsters' stats.
The second half is where things really start to get crazy. Typically, if both mages are fairly good at the game to the point where they can survive the first half, then the fight turns into a one-on-one magic duel between you and your opponent. You have up to 400 different spells at your disposal to wreak whatever havoc you want upon your opponent. However the 1-on-1 duel isn't just about sending out big attacks. It's also about defending yourself, using teleporting wind spells/ barriers made out of stone pillars/ healing light magic/ etc.
In many cases, a 1-on-1 duel between you and an opponent can last several times as long as the initial RTS fight between your battalion and your opponent's batallion.
There are only two problems I have with the multiplayer, and here they are:
1. The basic healing spell fills your HP up completely, and requires hardly an MP to use, and this is just when you first start out in the game. Sure this spell is good for you, but it's also incredibly cheap in multiplayer.
2. There is absolutely no way to get rid of the 10:00 time limit in multiplayer. It's required. Also, if a fight ends because it reaches the time limit, then the match is considered a draw. It's not decided based on which mage has the most HP left over, or anything like that.