Trickster Online currently has 3 different ways for Player Versus Player battling.
In Ceremonia, talk to Bunny Maid and give her 1 Pink Potion A. She will send you to the Waiting Room. Here, you can choose to battle 1 on 1 (talk to Don Giuvanni on the left, requires 3x Compound Waste) or enter the battlefield where any number of people is allowed to go in: talk to Rosemary and select Battlefield of Dessert or Battlefield of Garden. Each field will cost you 1k Galders to enter.
The final option is located in Phantom School Dungeon, which can be accessed through Shaman Girl Jia, who is right in front of the entrance to Phantom School 1-1. Simple talk to her, and she’ll let you in free of charge. Phantom Dungeon comes with monsters, whose levels are around 180. The monsters drop potions, galders, Phantom Weapons (e.g. Phantom Pugio) and Stones/Crystals/Metals 185. In this Dungeon, you are free to attack anyone, as long as your Status isn’t set on Peace Mode. On the right side of your screen, you will see your scores of kills and defeats.
Watch out, as the Ghost Books in Phantom Dungeon self-destruct. They tend to say “Guaah!” before doing so.
The Tritch, called Dark Ball, will frequently try to teleport you to Megalopolis.