I'm still trying to replicate this user's strategy. It's fairly similar to another video I tried to learn from. The main concepts in his strategy seem to be this:
- Spam the hell out of the refineries, don't bother buffing them
- Find a narrow passage in the rock formations on the map where the mobs will have to move through and build your main defense line around that. I would go so far as to say if your map doesn't have anything like that, just start over until you randomly get a viable landscape.
- Use Scarecrows, spreader and brick walls to direct the mob flow into tight funnels and bounce them around
- Use droids for mobile brick wall protection
After finally beating it myself, here's what I took away as some additional pointers to win the thing:
- Build a chokepoint. It can be a total roadblock, just make sure sure the mobs are sufficiently slowed down while in your towers' range.
- Use tangleweb. It will help greatly to keep mobs confused while inside your towers' range.
- Use droids to wear down the enemy before it reaches your choke point. This will help significantly with the big yetis.
- Focus on heavy weaponry, skip blasters. Regular, heavy and multiblasters just won't cut it. Instead go with assault, spread cannons and lasers.
- Buff your towers for range, reload and firing speed. Batteries don't help that much in my opinion and reactors take up too much space.
- If you can afford it, draw an additional line behind your chokepoint, even if it is out of range most of the time to prevent a breakthrough.
The mission will take about 30 minutes in total, the big yetis appear roughly every 5 minutes. I found the smaller, faster guys towards the end the more challenging adversaries, as their armor is raised pretty high.
When things get icky, quickly draw a line of blockade in front of your towers. Always watch out for smartbomb powerups, they will be your best friend in the large waves towards the end. Good luck!