Why not have a PvP system like Mabinogi. You right click request PvP with someone, and the opposing player can choose to accept. Once he/she accepts a window opens giving both players the option to lower damage output from 0-100%. Then after all issues are agreed upon, both players must click "complete". The battle then starts with a 5 second countdown. But since this is Maplestory, there should be an option where equips have no effect.

Mabinogi
IGN:Wrathofend
Server:Mari
Guild:Dawn
GuildWeb:www.dawndomicile.webs.com
Total lvl: 1100+
Maplestory
IGN:Wrathofend
Server:Scania
Guild:Darkrealm
Level : 7x