Night Walkers use fast and powerful attacks, using the darkness to their advantage. They are enhanced with the element of poison.
Level 14-16: Go up the levels of Henesys Hunting Grounds. HHG 3 is generally the best open empty spot. Since it is very difficult to find pigs in numbers without the ribbon pig alongside it go and travel across all towns except for Perion and kill everything killable. Another good leveling location is the map East of Kerning City, where you can easily kill Octopus and Green Mushroom, giving you quick EXP, although be sure to stock up on potions! Leveling should be extremely fast if you're funded with kumbis or better.
Level 17-19: Pig Beach. Your level 10 lucky seven is enough to kill pigs in one hit and ribbon pigs in two, and while it's not extremely profitable, you won't lose money, and will gain some from the occasional drops. And yes, nobody can ks you, not even a mage. Warning: The very irritating Iron Hog will spawn in Pig Beach occasionally. So watch out! If you managed to aggro it, cast Disorder if you have it.
Level 20-24: If you're going for the poor build, continue at Pig Beach. Training is going to get slower now, but bear it for now. If you're maxing Lucky Seven early, then go ahead and kill Green Mushrooms, and hope that the ever-elusive pan lid drops. A Better alternative are Bubblings in Kerning subway Line 1 they give the same EXP as green mushrooms but with relatively NO KSers.
Level 25-30: Green Mushrooms, or Horned Mushrooms at ant Tunnel. The former is more profitable, the latter is quicker, although you will lose money. You could also try Jr Sentinels, but it is not recommended. Zombie Mushrooms are also an alternative if you have Kumbi or better, as you can easily 2HKO them with Lucky 7. If not, stick with Horny Mushrooms. Wild Boars can be an option too if you seriously think you have enough money to burn on potions, and boars move quite quickly, which is more challenging.