Actually, the RA Tesla Trooper wouldn't actually "attack" the tower; you would right-click and he would walk over and "charge" it; more like a spell, really. What you
don't want to have to do is catch an attack each and every time and have to reduce it to 0 or replace the lost HP; just confuses the game.
Instead, pick any one of the "single unit-target channeling skills" (Pretty much just Aerial Shackles & Life Drain/Siphon Mana; the ability Channel could probably be perfect too), set all the pertinent stats to 0 (No effect), and then create two triggers along the lines of:
E - Unit starts//finishes effect of ability
C - Ability being cast = Tesla Power-Up
A - Add//Remove [powerup mode] ability to Target Unit of Ability Being Cast
That way, you can arbitrarily pick
any type of "power-up" you want to be applied to your towers. More damage? Pick an invisible "+X Attack Damage" item ability as the base. More attack speed? Pick an invisible "gloves of haste" ability to add/remove. Multi-attacks? Choose Barrage. An Aura? Spell Immunity? Etc. Quite a lot of options.
Haven't tested it, but the TheoryCrafting is sound. BTW, feel free to use this, but you saw it first
here, and you'll see it soon
here.
Dibs.
#20130712