The Vulture

This creature is a lie in wait or set a trap creature. It sits on the walls (not visible to the attacker when they scott you) of an area inside your base large enough for attackers to spawn in or on the outter most walls of your base then it rips the attacker apart as they appear. This creature should be paired with the Tesla coil because attacker will believe they can spawn in the area where the coil is. It will work well for low level beginners as they can cover the empty spaces in their base.

They should be priced so that you can outfit your walls with them to repel attacking troops and set the trap for anyone who would try to spawn inside your base. They just hang out on the ramparts of your base and attack as the enemy troops get in range

Or maybe you don't place them. You buy them and they fly onto your base and roost anywhere but they are drawn to the walls near tesla coils and open spaces inside your base where enemy troop can spawn

repeated bumps is against forum rules.

Kind of like a RULED OUT idea:

"*Stack def structures – ATs over walls, Teslas on top of barracks (truly hidden), etc."

I see you point. Lets say they're not invisible. They just roost on the wall and when an attacking troop gets too close they swoop down and peck them to death. I have an image of a Barbarian running wildly around the battlefield with 6 Vultures clinging to him pecking him :D