The idea is that you start the game with little to no hero bonus, but all towers gain bonuses either per wave or per level.
Starting amount: +0% to all stats (if this is too strong, maybe start between -20 and -10%).
Scaling amount: 1-2% per level or maybe 0.5% per wave.
The idea is a hero that starts off as a penalty, but gives good growth later. I'd argue for the per wave bonus, if it can be done as a per wave since the tower was built. Learning from watching.
Maybe since this is about learning, there could also be a +10% xp bonus to towers and maybe to wizard xp.
Title not set:
This wizard could also be named newborn babe, student or some other position of weakness and rapid learning.
Edit: formatting and:
I realize this is a bit like bookworm, but I was looking for something that would give the towers some attack speed and as well as xp.
Of thile attack speed makes stun and slow towers too strong, it could come wtith a -10 to -20% luck penalty.