I have finished the game and got the in-game achievement for dealing over 100 damage but did not get the kongregate badge for it. I decided to reload and do the final battle again in hopes of getting the badge. Now my mage cast "expand mind" but it had no effect. Attacks are working strangely by not being defended against but not landing either and for some reason my mage summoned another spirit warrior making two summons and without me casting it.
TBTabby: you need to build some collectors quickly (on high ground) then maybe a couple blasters to keep the creepers back until you build more collectors. You slowly move your line of defences foward and keep building collectors around and behind them. Always make sure your collecting more energy than your using so your turrets don't run out of ammo. If part of your base gets overrun don't worry about the collectors (and other things) in shallow ground around the overrun area, they will be destroyed no matter how many turrets are building around them. Build defences on the next higher ground and the creepers will be contained.
Turrets: Drones are only good mid-late game and should be used when being overrun and when pushing forward, don't use them as basic defences. The grenade turrets are alright if attacking higher ground but generally I would stick with blasters. Anti air missile turrets only need to cover the front line.
for level 17 you need to get the cell closest to the enemies and continuously connect and break tenticles from it to your cell furthest away, this propels it foward a bit ( sorry about spelling and grammar im tired and rushing this)