The idea is to starting in the mid game the build is based around the Spider+Rupture+Vulcano idea later turning into a Hugger+Rupture+Vulcano with some melee damage optimisation.

Here is my build in actionin the last few levels.

Unfortunately i wasnt able to screenshot the last skill tier, but i will tell you what to get!

This Guide begins around the time you have the spiders unlocked but gets a lot stronger with the vulcano skill!

The idea is that Spiders damage the wall building up Rupture stacks (each stack is x1 damage multiplier) with Vulcano costing 500k Mana but turning that into a x2 multiplier.

Once you get Vulcano you can start the build proper!

The sekeletons act mainly as shields for the spiders, the main damage dealers.

Then get the Spiders and Hells Gate, that with Vulcano is the focus if you can buy some damage boosting skills (Lv. 14, on the right) it will give you a stacking damage multiplier for each 100 minions you have summoned.
The Cake is boosting melee damage for Skeletons, Devils and Huggers with the first point being a huge 1000% and each consecutive a 100% bonus!
I am not sure if the "Zooka" is so good maybe get the insect plague instead it works great with Hells Gate.

Here just get the skill as soon as you can but the Gobchulate (Lv.23, mid) is not worth it!. Dont get it its my mistake thats still on there.

For the last tier get the Bonetsunami, at this point i had ~1200 Skeletons out what ended up at a multiplier of around x6000 !!!!

Here you can see some of my choices but i will sum them up:

• Mana Fang is key!!!
  
• Summon as many Skeletons a possible, the moment you get Volcano they will only farm Rupture and at the moment you unlock Hugger they will be useless!
  
• The second item is more or less up to you, i choose the extra damage.

The damage multipliers on the left in order:

• Rupture
  
• Hell Gates
  
• Armysize (not correct name)
  
• Volcano
  
• Fracturing
  
• Bone Tsunami (Late game skill, wall 96+)

At the end focus on the "Heighten" spell because it increases melee damage like Hugger und Skeletons do. Magnify also boost the Volcano spell