Well, this is pretty simple and I found out about it purely by case. Everyone who is lvl 20+ has heard of NoS or Necropolis of Sacrifice. Well, if you want to help one of your friends lvling faster, but he isn't lvl 20 yet (thus he cannot join Dawn or Dusk or enter the catacombs) there is a simple trick:
Make your friend stay on the beach below Langk Lizardman Barracs ... When you enter the catacombs, just find yourself a suitable room (I'm lvl 32 artisan with pole and brigandine set) to AOE place yourself onto a spot where you will be pulling the mobs and AOE them, then simply ask your friend to follow you. When he will be right on top of you, you can start pulling the mobs in that spot. He will get every % as if he would be in the catacombs wih you.
I lvled a human fighter from 15-20 in a couple of hours & getting 4% a room myself

Its a great trick, don't tell it to everybody
Notice1: Dont forget a healer or a lot of GHP.
Notice2: The map is almost always wrong, dont rely on it.
/if you like the exploit, please say Yay to the admin
yeah if you want to lvl just a lowlvl ... but if you want to do something for yourself then ... you do it like this.