The law of juggling and the U-defense in desktop tower defense

As you have seen from previous videos, juggling is required to get high score, and to survive the 100 levels. This is a study to find successful juggling strategies and to simplify juggling, so easy that nobody hates it anymore.

For various reasons, the line of creeps in your maze will grow longer and longer, making it impossible to block your creeps in the maze by selling and building towers in different places.

To be successful you have to minimize the line of creeps, and to be able to shorten the line.

Minimizing the length of the line of creeps is easy to say:

1. The creeps on the two entrance should enter you maze at the same time. For the worse timing, you have lines of creeps twice as long.
2. Creeps should come out at the same time rather than gradually, using the "send next creeps button".

What prevents the creeps from coming out altogether is the flying creeps. If two waves come out at the same time they will easily overwhelm your air defenses. So basically you sent 7 level of creeps together if possible and keep them in by juggling. When the air creeps are about to clear you send another 6 levels together, but time their entrance so that they will join the creeps already in the maze.

To be able to shorten the line of creeps in the maze keep you in an invincible position. For this I came up with the U-defense. But sadly, after I reinvented it, I spot something similar in the videos that was not obvious because of the fast play speed.

The maze shown is a straight forward implementation of a double U-defense. The middle 4x6 towers are about enough to deploy air defense in a mix of swarm, boost and snap towers. The lower right corner shows the two exits of the maze. One of the exist are always blocked. Since you can actually shorten the line of creeps, other strategy isn't that important, unless you reach the point of aiming at the highest score.

The critical tower are the two towers marked "g", which can be seen as a return valve by passing a large U shaped path. When the creeps enter the U, they are slowed down. When they passed the U and then returns because of blocking, if the U valve is open, the later creeps to return will catch up with the earlier creeps, shortening the line of creeps!

The timing principle is simple. When the first creep enters and exits the U, passing the g-tower the 2nd time, this g valve can be open at the exact time but no earlier. If the valve is opened earlier, other creeps will find a short cut and pass the first creep to lengthen the line of creeps. Now when the exit is blocked and the first creep returns, it will return via the g-valve, catching up with other creeps returning not from the g-valve. So the line of creeps is shortened.

The juggling sequence is very simple. One of the exits is blocked. When the first creep passes through the middle of the U, it's time to sell the valve and the blocking tower in the other exit at the same time. It's so simple you can't forget it, and there's no extra difficulty other than simple juggling. When the selling is complete, you block the current exit, so some creeps return via the normal path and some return via the valve. After the last creep returns via the valve, block it. Then rest a little and do the same for the other path. Note that this timing is for the maximum sell time. When selling is fast at the beginning of the game, you can sell the valve-tower and the block-tower later.