What were these pieces of literature that I forgot?

I say “literature” because I don’t remember if it was a slideshow, movie, book, game or other thing/experimental.

VARIATION 1:

However, I remember that it was about a mighty dragon in the early medieval era. The dragon hid in a cave or a dungeon of some type and killed lots of people, as dragons do. The king sent lots and lots and lots and lots of soldiers and men after the dragon but they all died for some reason.

Then a chemist man appeared and went to the king. He got everything set up, and when he went to the dragon’s nest he gave it some meat with some mysterious chemistry stuff inside. This made the dragon very thirsty, so when he went to get a drink of water, the water caused the stuff to make lots of gas or something so that the dragon’s stomach swelled up and exploded within seconds, killing the dragon.

VARIATION 2:

Same setup as the first one, dragon cave, dragon much kill, useless king’s soldiers, etc, but this time I think everyone just ignores the dragon and lets it have it’s food of a few villagers and sheeps every moon or so, until they eventually build up good enough technology to either kill it or put it on a leash and make it useful.

VARIATION 3:

Every 300 years or so, a batch of orcs/dragons/mystical beings appear with arrow/sword-proof armour and thick skin, where they quickly raid and pillage many towns and villages and steal a bunch of trophies, etc, until they get bored and leave, whereupon humanity then slowly rebuilds and that’s where most of the myths about great beasts come from, though most are highly exaggerated.

Anyway, the monsters keep doing this for quite some time until they hit the years of 1700 AD to 2000 AD, where humanity has somehow advanced to the modern age like normal, and the monsters still attack and get slaughtered. NO, it is NOT Salvation War, though I thoroughly enjoyed that series anyway, even though others have said it is awful.

VARIATION 4: Same as 3, but instead the monsters arrive at a totally different earth, one that did not survive the Cold War.
Thanks…