Requires tower stacking (Get AHK script). Requires cancel stacking (just go to place each tower you want to place in the stack in the right place, then right click to cancel, dont left click to place it. Then as you use the tower stacking script itll place it in that place you cancelled it in).

First wave: Auras (Ensnare, Str drain. On lower levels you can also electric), buff beam, 3x clouds (one south, two facing towards crystal usually one a bit north and one a bit west). 3x reflections that are all 1 unit length. Two infront of where minion walls would go and one near the stack/item box to stop projectiles from the south hitting heroes etc. 

If your stats are low and you're doing ruthless campaign for the first time, just do all wisp dens and 1 or 2 shrooms instead of cloud towers. Clouds are needed for survival but you'll struggle if your stats are low unless you just do all wisp dens in the DPS tower stack).

1. Main tower stack in the middle of the circle infront of the item box. 
2. Hermit's nature pylon and golem if required either to heal stack for survival AFKing or to help if stats are low.

3. Ensare + Str drain aura essential, electric aura can help in lower difficulties.

4. Minion walls are 9 archers + 2 spiders + 3 mages. Place an archer on the middle pillar top thing and just do 4 either side. Not essential but helps if you cant survive with lower stats. 

This works on lower difficulties with low stats and that alone should get you the stats/levels to do it higher quickly. Nightmare hardcore campaign is easy to complete with low stats and survival will farm you some good myths and starter transcendents. Ruthless survival will net you top tier myths, and pretty good trancendents with occasional supreme/ultimate drops. Not the best to farm but one of the easiest one-stack options to get into the later game. 180-240m XP per character for a full ruthless survival run.