You must have Skullgreymon.(Note:If you don't know how to get Skullgreymon look below.) Now train the Skullgreymon. You'll notice at Lv70-80 it will learn a technique Dark Shot. At Lv90-99 it must learn how to evolve BK(Black)Wargreymon,if it doesn't redo it again.

Note: It's better then Wargreymon.