The attack of the alchemist(merc) was taken. I dont think this was a good thing.
Yes, it prevents him from attacking, when you want to place mills, but the ability to turn of the attack was there for it...
There's a lot of easter eggs on the map, and without the attack, you cant get it with the alchemist.
I say that because its the only unit that has 6 slots of inventory.
Going to pick it up with your human or hero, would slow down too much the start.
I suggest to give it's attack back, along with the ability to turn it off.
That way, players would have the option if they want it to attack or not...
About the towers, I suggest creating new upgrades in the others tab.
The upgrades would work in stages. Could be added some requirements to train the final ones.
I think that 5 or 6 would be a good number. Each one would give all the towers a boost on their attack.
They could be very expencive, that way, it would be similar to the items for the heroes.
The upgrades should give enough damage to a group of 20~30 towers, so they could kill all 3 final bosses, by themselves.
Without any help from a hero.
The price set for each upgrade, would balance the stages of the towers. That way, it wouldnt become overpowered.