Spelljammer: Adventures in Space intends to take Dungeons & Dragons 5th Edition players off solid ground, into deep space, and further to the Astral Sea. This collection of three books contains everything that a DM would need to understand about new mechanics, everything to run combat in space, and everything a player would need to create a space-faring character. There's a lot to learn from these three books that aren't just applicable to a space adventure, but also to your more terrestrial Dungeons & Dragons outings. We'll cover a few Spelljammer: Adventures in Space DM tips here so you can know what might be an interesting idea to bring to your next game.
Spelljammer DM Tips - Anything can be from space if you just make it a bit weirder
The monsters included in this expansion are nothing to laugh about, especially when Boo's Astral Menagerie boasts 72 different creatures that you'll find drifting across the stars. But what happens if you don't want to settle simply for the monsters included in the book? The book gives the solution to this and it's simply to give any regular creature the "Unusual" feature. This simply means the creature now doesn't need oxygen to survive.
Lets take that a bit further though to see how else we can take something and make it weird enough to be in space. Before even touching anything mechanically there are so many ways you can alter a monster to make it just off enough to be new. Your players can be searching a far-off asteroid and run into what they would normally understand as an Owlbear but instead of having short feathers it could have plated leathry skin like a Pangolin. You don't need to worry about the sanctity of altering a stat block but a fresh experience has been made for your characters. You can also take inspiration from deep sea life for new features, especially if you're going for a horrific vibe.
Spelljammer DM Tips - Have some fun with gravity
A large part of understanding space travel is how gravity affects your ship, celestial bodies, and of course, the planets that you'll be traveling to and from. The Astral Adventurer's Guide has full details and descriptions on how a gravity plane works on any of the Spelljammer ships that you might be traveling the cosmos on too. If your characters are making their way through a certain magically charged area, possibly a place of Unraveling Magic from Tasha's Cauldron of Everything, or even through the lair of an evil Wizard who has a focus on Dunamancy from The Explorer's Guide to Wildemount. You could create a new puzzle or realm that uses the same kinds of mechanics to alter gravitational planes. Players could find themselves in an M.C. Escher-like scenario (good luck to the DM to even be able to describe this).
If you want to spice it up further there are rules for how weightlessness can affect a player's ability to move, as well as their ability to use melee weapons. Magical items or weapons that mitigate these effects could also be the goal of your players if you're interested in putting them at a disadvantage to start with, before allowing them to get the upperhand.
Spelljammer DM Tips - Create your own Ship and set sail
Traveling by boat isn't a new concept in Dungeons & Dragons in the slightest, and while there has been a lot to do with the mechanics of ship-to-ship combat and the way that they travel. Normally the blueprint for these ships is something you need to find online or create for yourself. Inside the Astral Adventurer's Guide there are full floorplans, features, and weapon diagrams for 16 new ships each more unique than the rest. If you want to get away from the standard-looking galleons and skiffs then the unique Turtle ship or the Squid Ship can really shake up what players might be used to seeing in their world. Those specific ships could even be used as an in-universe answer to submarines if your party ever has need for an underwater adventure.
Like with everything I love taking things a step further too. A lot of the ships included are based on other creatures such as a turtle, fly, mosquito, or spider. You can play mix and match with various room layouts and floor plans and pluck a well known animal from the world of Dungeons & Dragons or from our own and fashion your own themed ship for players to enjoy.
While there might not be as much that's so translatable from the world of Spelljammer into your terrestrial Dungeons & Dragons adventures the times that you'll be able to pull off a room with remixed gravity, or have your players step aboard a sea vessel in the shape of an Almiraj and describe every unique detail to the party they'll be in awe of the world building and set dressing in front of them. If you like our tips here and are interested in checking our how we've taken lessons from other sources be sure to check out our other features.