You should bring 4 level 5 hog riders in your clan castle. Alternatively, you can bring 4 level 6 balloons in your clan castle, but they will be targeted by the air defense so hogs are preferred for this attack.
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Lure the CC troops as usual.
Destroy 1 AD (air defense) near the core of the base with your lightning spells.
Destroy a semi-exposed air defense with your hog riders for your clan castle troops. You should drop your king first to distract other defenses from your hogs.
The hogs should have destroyed the AD so now spam your dragons like you used to be able to before the 3 AD at TH8 update! Should work because there is only 1 AD left just like there used to when there were only 2 ADs at TH7.
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Thanks for reading, and I hope it works for you! It is a really simple strategy for TH7s who want to get 3 stars in their war attacks, just like they used to before the 3rd AD at TH7 update. ;D