There are several ways to get crests. I suggest you attack lvl 5 wilds. If you dont mind losing 50 archers every attack, you can send 2k archers. If you do mind, send any unit before the archers (make sure the 1 unit attacks before the archers). Btw, if you do send a unit b4 the archers, ur chance of finding crests drops dramatically. So just attack wilds over and over again and hope you get lucky.
Note: There have been rumors where you can attack the same wild over and over again many times, even if the wild has 0 units, and you can still get crests. I have not ever found this true yet, but its a possibility.
You can attack the same wild over and over again
but you have to own it then abandon it for it to work.
Wave 1 - Suicide Squad to use up traps
Wave 2 - Main Attack
Wave 1 100 militia
Wave 2 4,500 Archers OR 750 Ballista (1st Wave) Losses
Wave 1 150 militia
Wave 2 5,750 Archers OR 2,000 Ballista (1st Wave)
Wave 1 299 Miltia + 1 Ballista
Wave 2 10,000 Archers + 1,000 Ballista OR 3,500 Ballista (1st Wave + 1 Archers)
Wave 1 599 Militia + 1 Ballista
Wave 2 15,000 archers + 1,600 Ballista OR 5,500 Ballista (1st Wave + 2 Archers)
Wave 1 1199 Militia + 1 Catapult
Wave 2 35,000 Archers + 2,500 Catapults (1st Wave +6 Archers & 50 Catapults)
OR 45,000 Archers + 3000 ballista (1st wave + 1000 archers & 400 ballista)