This tower is frightening. The best strategy would to be slowly leak creeps.
Starting at 200% health:
Falling down to 180% health means +1 head, for 4 total heads.
Then 162% means 5 heads.
146% is 6 heads
132% is 7
119% is 8
107% is 9
96% is 10
86% is 11
77% is 12
69% is 13
62% is 14
56% is 15
50% is 16
45% is 17
41% is 18
37% is 19
33% is 20
30% is 21
27% is 22
24% is 23
22% is 24
20% is 25
18% is 26
16% is 27
14% is 28
13% is 29
12% is 30
But wait, this is getting dangerous. Let's drink a Vital Dust potion. Now we're ready to leak more creeps and get 10 more attacks. Each Vital Dust could give +10 attacks, depending on how careful the player is.
That's a wild number of attacks.
I really like the concept though :-)
We could maybe adjust it to whenever the wizard loses a total of 10% health to reduce the amount of abuse a little?
Or 10% current health (capped at minimum XX% health)
Balance testing could help decide what a balanced XX is. You propose 10