The linke below might help too. Several people published their winning defense builds. Lots of legendaries in play in most of them, but that is to be expected I think. Hang in there and keep building! Keep in mind the rules the AI follows as well. It isn’t incredibly bright, but you can play to it’s strengths. Focus on simple builds without too many choices. Remember the AI fires an ability almost as soon as it is ready, so make sure whoever you place first you want to charge and fire often if they are blocking later units. For example, the goblin charging and firing as often as possible is key to the team I posted. So the AI doesn’t really hurt itself too much when it does so.
-Razlath