Leaks. How to avoid them.

Good topic, Kostya! You hit the nail on the head with these strategies!
I'm certainly not some super cool online hero, but I'll add my two cents to support your topic.
With just one Hydra, you can take on the maximum number of creeps by attacking the Vampires. All the other inhabitants of the crypt will just stand there and wait for the battle to end.
With two Hydras (1 stack) plus single units, you can take the maximum Hive. Without the single units, one Hydra will be lost. I haven't tested the hero's stats, but I remember that 3 defense is enough.

It seems it's not such a great strategy after all, Kirill, considering how little "popularity" it has :)!
And about the Hydras - good job writing that. I just wanted to clarify: did you mean the crypt on the swamp (where the Hydras' speed is 5+1=the Vampires' speed) or on neutral ground?
As for your second example, I haven't tested it myself, but our forum member Oelm has already established that the maximum Hive can be taken with two Hydras without any single units and without losing a Hydra, if you take it in "Quick Battle" mode, which is set in the settings window. By the way, I can add that it's also easier to defeat Archers in Quick Battle mode than "manually" - there are usually fewer losses, although this is not guaranteed:) ...