Upgradeable buildings with spells

What is the best way to go about upgrading the spells as the building upgrades...

Kind of like a Tower in a TD... To give it stun you would have to give the tower bash... and everytime the tower upgrades you would increase the chance of bash by leveling it up... what's the best way to go about upgrading the spell everytime the tower upgrades.

Also for a frost tower what would be a attack and movement speed reducer?

Have a new ability for each upgrade. Or have one ability with multiple levels, and when the building finishes upgrading, increase the level of the ability with a trigger. You seem to already have the answer to your question, not sure what you're looking for...

I was just wondering if there was a easier way that I didn't know of.

Unfortunatley there is no easier way then to have different abilities.

Okay thank you...

And would anyone know what spell reduces movement and attack on attack

Slow Popison woeks easiest since you can easily change hiow much it slows.

If u want an AOE slow use the Frost Breath ability.

thanks