After trying all 3 classes as well as a bunch of combinations, I must say this game is pretty balanced. I preferred the engineer though since I'm more of a sit-back and pick off the remainder player lol, but an engineer setup made challenging mode a breeze most of the time.
For lvl 4 it helps to know the terrain and what mountains the spiders have to stop at (i.e. can't fully cross) so that you know how to properly space your units (you don't always have to move your units if it means the spider will come into your range but will still be unable to hit you; if you will be attacked no matter what, place your tanks on a forest; if you get the spiders in a chokehold/stalemate, use this time to repair). Around 50% of spiders go for one ranged unit, and 50% go for the other. Keep this in mind and remember the spacing =P
max out begging, max out combat in conjunction w/ dungeon exploring and selling useless items, and eventually you'll be finding yourself with 5,000+ gold without needing to work at all, and a character that dodges almost everything. Remember to 1) if you've worked or studied, try to use the remainder of the points for exploring the dungeon, 2) if you found the special item in w/e dungeon, don't leave the place! It will waste a week. Get more loot instead, the more $ you have the less weeks you will waste. When you feel you have a lot of $ rolling in, only buy the most expensive resting place, 3) Get a few stamina points when you can -- sometimes you'll get them randomly when you rest at the most expensive place.
4) Following this, you will also end the game with pure sin.
5) Using this, you should also be able to end the game with all gold items =)
Peace.
30 Energy Upgrade,
16 Stability,
Max projectile (even though I only used 2 types by then -- the top-right white one, and occasionally the black one that makes the black hole),
Level 2 Grav manipulator,
Shockwave,
Gravity trap,
Shockwave tower.
The combo worked wonders. Focusing on energy upgrade really helped, in the final level, I spammed ammo and never ran out of energy. Anyway, 5/5
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