Favorite Target Spell

The title says it all. You have a spell that you either pre program or program right before you place it. All troops that walk through the spell range will have their favorite targets changed to whatever you want. I haven't decided if it should be defense specific (Ex: Favorite Target Air defences) or if it should just be any defense at all. I also haven't decided if it should be resource specific. It might be OP if Hog riders favorite target was Dark Elixir or gold.

Unlocked at TH 11 spell factory lvl 6
Training cost 50,000 elixir. No upgrades
Or maybe if you upgrade it then it can go from being non specific to specific, let me know.
Lasts for 7 seconds.
Takes 50 mins to make.

Lemme know what you thing.

THX