How to kill Black Dragons?

I don't know about everyone else, but playing as Death, I put Vampire Touch on my skeletal dragons and with 15 skeletal dragons I wiped out 35 Black Dragons (and the rest of the army equivalent to 35 Black Dragons, i.e., as many as you can get by gathering 35 Black Dragons) without losing a single one (Well, rather they were lost, but everything was restored with the next bite). My friend almost fainted (My friend plays well). He later thought I was a cheater)))

P.S. After the battle, no one was left except the dragons, not even the hero - that's kind of a side effect, but the main thing is the dragons are defeated.

fifteen skeletal ones is all well and good... but you should have read this thread.
at least the first post.
the question is about defeating neutral BD as early as possible, for example in the Dragon Utopia - you don't need 35 - such a number of BD is rarely seen anywhere - the standard amount on expert is enough: 10-15 neutral BD - how to kill them at an early stage of development, with what minimum army?
and when you already have an army, especially when level 4 is built and upgraded, and heroes are leveled up, it doesn't cause much difficulty.

P.S. the fact that no one survived except the skeletal ones is a serious problem - heroes need experience;)