*PLEASE NOTE* I tested this build with two Summoners, one had an Apprentice Guardian and Huntress Guardian, the other with a couple of ToTs. I also did not upgrade anything with the exception of the two Buff Beams, so you can do this with MUCH lower stats than what I have (the stats shown in required stats). This build works well for dice farming, but it has been tested for normal survival/mixed mode clears as well. 

                           - Upper Core -

-Aura Stack offset to the East side of the Crystal

-4 DU Physical Wall with a 1 DU Reflect in front

- 4 DU Buff Beam placed on the Phys

- Gas and Inferno traps placed on the East side of the Crystal (Tower Mover recommended) 

- 1 DU Reflect covering the Crystals' West side

                         - Lower Core -

- Aura Stack offset to the North side of the Crystal

- 4 DU Physical Walls on the East and West sides (East as far against the edge as possible, West put against the giant black ( ͡° ͜ʖ ͡°) pawn piece)

 - 2 1 DU Reflects put in front of each of the Phys Walls

- 4 DU Buff Beam with 5 Lightning Towers and 2 Deadly Strikers, facing Southeast and West

- Ethereal Spike Trap offset to the South side of the Crystal. Move it with a Jester that has 0 in T. Range against the Crystal so it is in-between the Phys Walls

This isn't really an AFK build as the lower Phys Walls can get slightly damaged and required one Flash Heal, but with an Imp, higher stats or even one or two upgrades I am sure it would work wonders. Good Luck!