GENERAL NOTES:

• This build can be edited a few different ways. You can switch two of the lightning towers and the ethereal spike trap for two more deadly striker towers facing east and west. You could copy Manyu's build but with no MU. I've edited this build a lot and still not really arrived at one that I like the most, so I'll provide links to unlisted pages of other variations I've used. ^{5 6}
• I've been able to run this with only upgraded buff beams and a guardian summoner with 4 people with my stats. (5-6k mains, ~3k sides) Tinker with how much you upgrade and how much you boost to use as little effort as possible.
• The XP Per Run number was as host with no core damage or player damage. The Time Per Run number was my fastest run, but I'm sure others better than me can get it lower.

FIRST RUN NOTES:

• The bottom physical beams go right in front of the crystal. Due to ogre aggroing,the crystal should not get damaged much if at all. (I've only had the crystal get hit in similar builds on later waves of survival, and it was not often even then.) 
• If you have trouble with this build, I suggest using a guardian summoner or tower boost monk.
• To build this efficiently and repeatably, stacking is required. (AutoHotKey, the keyboard macro program commonly used to stack, and a script for stacking is linked below.) ^{1 2 3 4}

¹ AutoHotKey: https://www.autohotkey.com
² AHK stacking script (Windowed): https://pastebin.com/Nq6MTv90
³ Stacking script (Fullscreen/Windowed mode as Administrator): https://pastebin.com/27h8eTCw
⁴ Video on stacking: https://www.youtube.com/watch?v=TsIMZRLdL18
⁵ North Core Build v1: https://dundefplanner.com/map.php?load=655
⁶ North Core Build v2: https://dundefplanner.com/map.php?load=656

Hint 1:
Suggested place for tower boost monk (arrow shows approximate direction, stone's throw reccomended )

Hint 2:
3 DU physical beams. Stop ogres aggroing the DSTs and distract the harbingers.