Oooo I like the ant idea. How about if it has the ability which allows all ants to gain attack damage based on the sum of all ants' kills. Make it into a yellow or blue the least.
I really like the mole idea. With many hill towers and one mole, there would be a large number of items that could be equipped. I think it would be best to treat the group of molehill towers like an expanded Mr. Iron. Each molehill expands the inventory and gives more stats, however, only 4-6 unique items or set items can be worn by the whole molehill group. This would likely need similar balancing to Mr Iron.
Sticking with one mole is probably best, but in case it isn't strong enough, I have a couple ideas.
There could even be a family of moles of 1 mole isn't strong enough.
Family idea: each new mole requires 1 more molehill than there are moles. So 1 molehill gives the first mole, 2 more molehills are required for the second mole, three more for the third mole, etc.
1 - 1
2 - 3
3 - 6
4 - 10
5 - 15
6 - 21
Royal mole: unique mole card that is a stronger mole. A bit like king arthur or Muli. Maybe gains some of the item or potion effects from the other molehill towers. If the family exists, then he joins the family. If it is solo-mole, then he would replace the base mole. He would likely be a slower, harder hitting version of the mole that could scale into the late game. E.g. ~2x damage, but ~2x attack delay.
