Bonus on any one tower type chosen by the player.

So I was thinking that instead of creating a new tower type in order to increase variability in bases, Supercell could create special bonuses for each tower type. This would make it so you can either choose all of one tower type to have that special ability or just one tower in your whole base. I'm not sure which would be healthier for the game. I feel like just one tower with a special ability would be cool enough to make things a lot more interesting, yet not powerful enough that it would break the game.

But here are some of my thoughts:

• Cannon:
  
  • Cannon balls pierce through enemies in a line (hitting up to 5) dealing 20% less to subsequent units (due to the cannonball slowing down)

• Archer tower:
  
  • Fires at up to two targets at once, but at a slower rate of fire due to splitting the archer shots (Only available once the archer tower has more than one archer)

• Wizard tower:
  
  • Increased attack radius
  • Increased fire rate

• Mortar:
  
  • Fires cluster bombs-Once landing and exploding, extra bombs explode in a smaller radius for an extra 50% of the mortar damage

• Xbow:
  
  • Ramps up in damage infinitely, but resets on different targets (having many many many arrows in you would surely hurt increasingly over time)

• Inferno:
  
  • Freezing spell duration is halved from subsequent freezing spells (Extreme heat)

• Tesla:
  
  • Attacks will chain to close by enemies dealing 50% to subsequent enemies (up to 4)

• Air Defense:
  
  • Shoots flak- Grouped enemies take area of effect damage

Just some ideas! Maybe my ideas suck, but as a community, I bet we can build something good out of this.