Stats are just what I have, it is not unlikely that you can do this with less but I have not verified.

Very nightmare difficulty looking build, but all the builds with 1 stack were too flimsy for me and I feel less stupid building towers at every crystal than having to make minion walls at half of them.

Might be able to get away with not using tower stacking given how small the stacks are, not that I assume most people are playing on ruthless without using stacking.

Wave 1 build the auras, beams, and warden towers

Combat 1 bring upper (adept or jester, don't use upgrade aura) to upgrade the beams, and the towers if you're feeling spicy.

Wave 2 build the golems

Consider bringing DPS chars for later waves once the beams are upped, would recommend paying attention to the bottom crystal, there's not really a good spot to place the golem there that doesn't get hit by ogres from the door above and that's with my stats.

Also consider adding minion walls if you see a core getting smacked.

Dunno if you can bring splits in easily with this, but the rewards from this map do not to me appear good enough to warrant bothering with, so that is up to you to experiment with.