You can enter a High-Roller dungeon as a group, with a maximum number of 3 members. High Roller dungeons have an entry fee of 100g per player. There will be no kill-feed or in-game timer, although you still have the progress bar that fills up red as time goes by, giving you a rough estimation of how much time is left. There are better drop rates for high quality gear. The only way to obtain unique grade items are from High-Roller dungeons. Monsters will appear at Elite and Nightmare grade.