1. Starter waves. We see this in all the games. It's just the warm up phase. Easy. Get used to your tools and the space.
2. The suddenly tough run. All seems easy and predictable until a new baddies tors the board. You have to go from lax mode to something more serious. Autopilot off.
3. The board changes. Even if the round is tough, you've been managing, even winning... but then the space itself becomes your enemy by changing the features you've counted on for success. A new path is cut by a boss, and that throws the relationships between your towers...
4. The sudden ease. After a very hard run, or set of rounds, you suddenly find unexpected respite. The bosses are easy to beat. You win.
Sent from my Orac M-BRANE FieldTouch (Plus).