Giant monsters! Ever since humans realized that we might be terrifying to small creatures, we have been obsessed with the idea that we could be the small creatures. Of course we have had to contend with large creatures, but… what if they were bigger?

Being the gaming-obsessed pedant that I am, I must therefore ask the question: how does this relate to Tabletop RPGs?

Because behemoths are a unique change to the way that encounters work. Not only are they great world elements which can have far-reaching consequences, but for combat-centric games it can be pretty challenging.

World/Story

The often devastating or legendary effects of a large creature can easily be used to create wide-reaching effects and hooks. Not just the immediate effects such as destruction and natural-disaster scale ruin, either. As a result of a giant creature’s presence, you can also deal with:

• Rampant famine from loss of crops/herd animals because the behemoth has eaten or destroyed them. Banditry and desperate mobs could become a huge problem.
• Mass movement of people after destruction of populated areas. The movement of many refugees puts strain on unprepared systems (housing and food at the least), and even cultural differences could crop up, exacerbating tensions.
• Ecosystem imbalance as a result of a behemoth’s wake. Forests can be flattened. Flooding can result from natural and artificial dams being burst, and rock formations can be shaken loose, endangering those below. Animals may also be pushed into new territories if their own is disrtupted.
• Mass religious hysteria as the established religions and small-scale cults seek to find meaning in the existence or sudden appearance of the behemoth. There may be new holidays or expectations which get in the way of the players, such as required conversion or donations in population centers. Religious authorities may also try to prevent the removal of the behemoth, as they might see its presence as sacred.
• Not to mention the more fantastical ways a behemoth could affect the world of play; arcane auras which prevent magic from working for miles around, residue which spreads disease or renders areas barren, or a voice which causes distress or madness to those who hear it.

Combat

They’re the size of a castle (at least)! Fighting them is going to be a challenge.

Often times, you can’t even really fight something that big! Even the most powerful attacks and spells available to human-sized characters may not penetrate the skin of something of the behemoth’s scale.

Often times this can be compensated for with high armor and an ungodly amount of hit points, but… even then it doesn’t really make sense. Can large dinosaurs be killed by spears and spells? Perhaps, but you need a solid plan to even give you a chance (ancient humans would chase mammoths into pits for easy killing, for example). Anything larger than that, and it’s like cockroaches trying to kill a healthy person. It happened in Creepshow, which was a fantasy horror film, but is not exactly believable if you think about it too much. Even high-level characters can only do so much.

Shadow of the Colossus had players climb all over the bodies of the beasts to reach a weak point. Other stories have multi-stage boss fights, which can break down the process pretty well.

I make no secret that I prefer a well-crafted plan, though. Physical interaction with a behemoth, something which exists at such a fundamentally different scale, would be more akin to interacting with a landslide or a raging river than a living thing. Such creatures must be approached entirely differently than normal encounters. I’d even remove any concept of “hit points” or “killing” the thing through conventional means altogether.