The longer a campaign lasts the more and more likely it is to involve planer travel, whether this involves conquering demons on their home turf or nipping into the realm of faerie for a talk with the Summer Queen. Finding your way into these mysterious realms can be a tricky affair, though one that can be made a little easier with the use of Astral Projection.
One of the most complicated spells in the game, Astral Projection allows the caster and up to eight willing friends to leave their bodies and journey into the Astral Plane. While there they assume a semi-real form that acts like their conventional body for all practical purposes. They also get to bring along their equipment – or at least the astral form of their equipment, which gets weird when you think about it metaphysically (so, do the swords have souls?).
Their actual bodies, meanwhile, stay exactly where they were when the spell was cast. While there they don’t age, breathe or require food, which is handy for those long trips through the planes.
Even better, if your astral form gets attacked by rampaging demons the damage doesn’t transfer over to your actual body. You can even get ‘killed’ without suffering any ill effects beyond waking up in the real world.
This doesn’t mean that you’re completely invulnerable, however. When you get bumped into the Astral Plane you’re still linked to your meat-form by a magical silver ribbon. If this ribbon gets cut (by the special silver swords wielded by Githyanki corsairs, for example) you drop dead.
Of course, this is mere mechanics, and doesn’t really explain why you’d want to float around in the Astral Plane in the first place.
The main reason is to use it as a stepping-stone to another plane altogether. The standard D&D cosmology sets the Astral Plane up as the ‘sea’ that separates all the others, with swirling colored gates acting as the entrances and exits. In theory, if you wander (float?) for long enough you’ll eventually find a way into just about any plane you would care to name.
This doesn’t quite answer the question completely though. Astral Projection is a 9th level spell, so by the time you get access to it you’ll almost certainly have access to Plane Shift and Gate, both of which allow the caster to hop directly to their target without having to mess around with any intermediate stages.
Both of these are technically much easier to use, but have weaknesses. The biggest of these is that it can be relatively simple for a powerful entity – such as a Fey Lord or an Archdemon – to close off their plane to them. Astral Projection is slower and tougher, but is almost impossible to completely defend against.
This means that while it’s not the kind of spell that you’re going to use on a whim, it may be something that you base an entire adventure around. Which is exactly the kind of plane-shattering power you expect from a 9th level spell.
If you need to travel the planes and can’t use Gate for one reason or another, this is what you’re going to have to fall back on. Less of a spell than a plot point that requires a 9th level slot, but that’s hardly a significant flaw.
Casting Time: 1 Hour
Range: 10 feet
Components: V, S, M (for each creature you affect with this spell, you must provide one jacinth worth at least 1000 GP and one ornately carved bar of silver worth at least 100 GP, all of which the spell consumes)
You and up to eight willing creatures within range project your astral bodies into the Astral Plane (the spell fails and the casting is wasted if you are already on that plane). The material body you leave behind is unconscious and in a state of suspended animation; it doesn’t need food or air and doesn’t age.
Your astral body resembles your mortal form in almost every way, replicating your game statistics and possessions. The principal difference is the addition of a silvery cord that extends from between your shoulder blades and trails behind you, fading to invisibility after 1 foot. This cord is your tether to your material body. As long as the tether remains intact, you can find your way home. If the cord is cut —something that can happen only when an effect specifically states that it does— your soul and body are separated, killing you instantly.
Your astral form can freely travel through the Astral Plane and can pass through portals there leading to any other plane. If you enter a new plane or return to the plane you were on when casting this spell, your body and possessions are transported along the silver cord, allowing you to re-enter your body as you enter the new plane. Your astral form is a separate incarnation. Any damage or other effects that apply to it have no effect on your physical body, nor do they persist when you return to it.
The spell ends for you and your companions when you use your action to dismiss it. When the spell ends, the affected creature returns to its physical body, and it awakens.
The spell might also end early for you or one of your companions. A successful dispel magic spell used against an astral or physical body ends the spell for that creature. If a creature’s original body or its astral form drops to 0 hit points, the spell ends for that creature. If the spell ends and the silver cord is intact, the cord pulls the creature’s astral form back to its body, ending its state of suspended animation.
If you are returned to your body prematurely, your companions remain in their astral forms and must find their own way back to their bodies, usually by dropping to 0 hit points.