especially after many attempts in single-player.

Climbing into an unknown crypt in the grass is extremely dangerous in a real online game.

Examples from single-player games where it works on the 10th attempt don't convince me.

Well, it's a bit of a lie :D :)

I took the crypt on the first try, and it took ten tries to get a screenshot when the skeletons weren't attacking the level 1 units, but were moving towards the archers. Which was extremely rare. (let's say a more challenging scenario)

Of course, this technique isn't universal and doesn't claim to be academically sound; I just wanted to show that the crypt can be taken (specifically in an online game), and there's nothing special about it. I think everyone, regardless of who they are, would have a similar technique: pixies (or, if there aren't any, level 1 archers block the vampires and skeletons) while the main group of archers shoots at the vampires, spearmen attack the skeletons, and a level 1 unit distracts the zombies.

and the crypt would definitely be taken; the moves would just be slightly different.

Taking the dwarven mine, on the other hand, is difficult. They have high morale :D And the undead are very predictable...

PS: And no one is trying to dissuade anyone; it's up to each player whether to try or not. Getting the maximum crypt for a Castle is a common occurrence, but if you don't want to, you don't have to risk it. Although the probability of encountering it is only 10%, which isn't too high.

(Maybe Dirty will write about how to take them with un-upgraded archers? :) I would be very grateful)