Irregular Webcomic! #3018

Red dragons, as every Dungeons & Dragons player knows, are the sort that breathe fire, and therefore have immunities to fire-based attacks. Those immunities differ with edition of the game:

In Basic Dungeons & Dragons, red dragons are totally immune to normal fire, and automatically make their saving throws versus magical fire, which usually means they take half the normal damage.
In Advanced Dungeons & Dragons (1st Edition), the immunity is rather weak, amounting to a mere -1 penalty on to hit rolls to attack the dragon with a fire-based attack, and a -1 on the total amount of damage rolled. (Yes, I had to read the rules twice to make sure that's right. I was expecting an additional note saying that it's -1 per die of damage at the very least, or per hit die of the dragon, but no, there is no such note that I can find in the Monster Manual. The upshot of this is if you hit a red dragon with an 8-dice fireball that does say 30 points of damage, the dragon actually takes 29 damage, or 14 if it saves. That's pretty lame, really.)
In Advanced Dungeons & Dragons, 2nd Edition, red dragons are totally immune to all forms of fire, natural or magical. Now that's what I call immunity.
In Dungeons & Dragons, 3rd Edition, red dragons are again totally immune to all forms of fire.
In Dungeons & Dragons, 4th Edition, red dragons now have Resistance to fire, which grants them various levels of protection that improve as they get bigger and older. At the high end, it's effectively total immunity.

But aren't dragons green, you ask? Sure, there are green dragons in Dungeons & Dragons, but they don't breathe fire. They breathe poisonous/corrosive gas - specifically identified as chlorine in early editions. Because we all know the traditional fantasy stories of brave knights fighting dragons that breathe chlorine on them.

But wait, there's more! Not satisfied with two different types of dragons, there are dragons of three other colours too:

White dragons, which breathe "cold".
Black dragons, which breathe a stream of acid.
Blue dragons, which breathe lightning!

[Aside: If you know Dungeons & Dragons at all, then you know all this already, as second nature. If you don't, then I should add this I Am Not Making This Up disclaimer.]

But wait, there's more! These are just the evil dragons! There are also good dragons! To distinguish them from their primary coloured brethren, the good dragons are metallic, and each one has a choice of two different breath weapons:

Brass dragons, which breathe two forms of gas, one that puts victims to sleep and one that causes fear (the fear gas was changed to simple fire in later editions).
Bronze dragons, which breathe either "repulsion" gas or lightning.
Copper dragons, which breathe either "slow" gas or acid.
Silver dragons, which breathe either paralysis-causing gas or cold.
Gold dragons, which breathe either chlorine gas (changed to weakening gas in later editions) or fire.

But wait, there's more! Some people, not satisfied with the limited palette of the original dragons demanded to know where the yellow, purple, orange, and brown dragons were. So they invented such things, and several saw publication in various gaming magazines, eventually making their way into official rule books. And then the metals seemed under-represented, so things like iron and mercury dragons appeared.

But wait, there's more! Around the same time, people realised that the rich dragon mythology of China wasn't represented, so a new class of "oriental" dragons appeared. River dragons! Earth dragons! Sea dragons! Spirit dragons!

But wait, there's more! And at this point I shall simply point interested readers here, to save myself from typing another 3000 words.