Four Lanes is a dungeon where you have to work together.
It depends exactly on the position how you enter the dungeon. All people are teleported to positions 1-4 one after the other at the beginning, just as you enter the teleporter.
When the players on each lane have killed their mid-boss, they are teleported together again. There, the process repeats itself, with another mid-boss waiting at the end.
If the lanes were cleared, all 8 players will be teleported to the last dungeon area at the end (right botton side). There another mid-boss is waiting.
If all mid-bosses from ALL levels were cleared, the final boss spawns (Mystic Crazy Bull Boss) at the end of the dungeon.