Duel in Monster arean (Like 4 team have a competition to hit monster)
Or some funny quest, may be team fight 5-6 vs 5-6
But need consist low level player (<100, D1, D2, D3, D4 form a team)
May be add some hitting Big Boss Event! (real difficult and dangerous big boss, not like now in maze one)
I think server need improve in something other than Dual, Up level, Rares and PK other!
(PK, Already hv normal arean, duel, war, abyss, undead, BM and One on One, team pk event)

In my opinion, D5 should not be open forever!
Because D5 is completely End Game!
What the motivation and reason for a player to play and login with a D5 full level rares and TT character??
Now, Many D4 quitted and afk or didn't login long time already,
if open D5, server will become more worst and empty!

Just my own view!

