Can a portable hole be used on a shield?

Question

If I fixed a portable hole on the front of a large flat shield, looking at the front of the shield, I would see a a 5 foot deep hole. BUT, looking at the shield from behind, would there also be a hole? Would the back be flat and untouched?

Would arrows shot into the hole re-appear 5 feet behind me? Would they just disappear?

I'm sure standing behind the shield, the arrows would not hurt me, as the ground or walls a hole is affixed to are unharmed after the hole is removed, so no permanent damage is done.

From the front, would the hole be limited by the thickness of the shield? Would the hole extend 5 feet back through empty space leaving a hole in my torso?

Would the hole GLUE things into a fixed position behind it? Like an invisible thumbtack made of negative space? Because a hole in a wall opens a space to hide in, crawl through, but how solid are the walls? you cant go sideways inside a hole, but is this because you are in a rock wall, and the unaffected rock is blocking your path? or is the hole itself the unmovable wall? Would there be no resistance, if there was no physical material blocking your path? i.e. COULD an outside object enter hole-space from the side, if there was NOTHING there to block entry?

To make positional questions easier, z-dimension is the depth of the upright hole, front to back, and x is shoulder to shoulder, Y-dimension up and down.

If I stood behind the shield (say, 5mm thick?), would the dimensional hole cause me to be separated from my lungs? If so, would they still function on the other plane? Would blood flow cross the threshold in x/y directions unhindered? Would a solid force stop my heart/lungs from oxygenating the rest of my body? Would it continue to work as expected, but just do so invisibly? Would I be "thumbtacked" into position and held, until someone in the front peeled the hole away? Could I come and go from behind the shield at will, because the dimensional adjustment only applies to the front surface of the shield along the x/y axis' leaving the back unaffected?

Answer 1

The description of portable hole says a portable hole

...unfolds into a circular sheet 6 feet in diameter. You can use an action to unfold a portable hole and place it on or against a solid surface, whereupon the portable hole creates an extradimensional hole 10 feet deep. The cylindrical space within the hole exists on a different plane, so it can’t be used to create open passages.

A narrow reading of this text would suggest that you can't put a portable hole on a shield unless your shield is 6 feet in diameter. (Otherwise you haven't placed all of the portable hole "on a solid surface", so it doesn't activate its magical powers.)

Let's assume that you could get around this — for example because you had a very large shield, or a very small portable hole, or you managed to get the portable hole to activate while partially folded up.

A portable hole is very much like a bag of holding, so a good way to think about this is if you had opened up a bag of holding and you were waving the open mouth around.

The space within the hole exists on a different plane — essentially there's now a teleportation gate on the surface of your shield, and anything that touches the teleportation gate gets partially teleported to a 10-foot cylindrical space on another plane of existence. It is not possible to enter or interact with the cylindrical space, except by going through the teleportation gate on the front of your shield. So the cylindrical space does not harm you, affect you, or interact with you, unless you reach around and stick your arm through the front of your shield.

Striking the back wall of the portable hole will have no effect on the wearer. Striking the back wall also won't damage the hole. (If you were using a bag of holding, it could get "overloaded, pierced, or torn", destroying the bag. Portable holes do not have this weakness.)

I'm guessing this is pretty convenient in combat, because any blows that strike the shield no longer impart their force against your shield arm — instead the attacker's sword goes slightly into the extradimensional space. On the other hand, it might be possible to damage the portable hole if a sword blow strikes against the edge of the effect. It's certainly possible for a creature to peel the portable hole off your shield and run off with it. Lastly, there's a small chance that someone could throw a bag of holding into your portable hole, which would destroy both items and teleport you into the astral plane.

Answer 2

Well, of course it is going to be up to the GM.

If it were me, you would need to spread out the hole to its full 6 feet in order to access the extra-dimensional space.

So you would need a six-foot shield. Maybe a giant's or something.

On the other hand, if you had a portable hole differing from RAW, say 2 feet, yes, it would work. It would be weird, but it would work.

Things thrown into the shield would not be felt by the wielder. The interior "surface" is extra-dimensional in nature and is not particularly hard or soft or cloth or anything else. Something thrown in wouldn't automatically fall out, but if the shield (and hole) were held whether accidentally or on purpose facing down, stuff might fall out.

From the back it would appear to be a normal shield. The hole wouldn't affect anything behind the shield in any way.

Attaching the hole might be problematic. If I were the GM, it would be a case of the player tries something, the GM narrates the results. Tacks or staples might be difficult to put through it, and if you could, it might not be good for the hole. Although since the backside is cloth, I suppose glue might work.

It's a pretty clever idea.

Answer 3

I want to offer a slightly different reading of the text. Here is the description of a portable hole, and some emphasis (mine).

Portable Hole: A portable hole is a circle of cloth spun from the webs of a phase spider interwoven with strands of ether and beams of starlight. When opened fully, a portable hole is 6 feet in diameter, but it can be folded up to be as small as a pocket handkerchief. When spread upon any surface, it causes an extradimensional space 10 feet deep to come into being. This hole can be picked up from inside or out by simply taking hold of the edges of the cloth and folding it up. Either way, the entrance disappears, but anything inside the hole remains.

The only air in the hole is that which enters when the hole is opened. It contains enough air to supply one Medium creature or two Small creatures for 10 minutes. The cloth does not accumulate weight even if its hole is filled. Each portable hole opens on its own particular nondimensional space. If a bag of holding is placed within a portable hole, a rift to the Astral Plane is torn in that place. Both the bag and the cloth are sucked into the void and forever lost. If a portable hole is placed within a bag of holding, it opens a gate to the Astral Plane. The hole, the bag, and any creatures within a 10-foot radius are drawn there, the portable hole and bag of holding being destroyed in the process.

There is some issues you should take note of...

1. To answer the majority of your questions, it creates an extra-dimensional space. Nothing appears behind you or anything of that nature. I'd almost think of it like holding a big box in front of your character - what goes into the box, is simply in the box.
2. The inside of the portable hole is made of cloth (this is an assumption, based on the circle of cloth used to open it and the comments in the description). I think it is assumed that shooting something sharp into it will cause it to rip (effects, unknown).
3. Although not specified, it does not state that the hole needs to be entirely unfolded. Just simply that it needs to be placed on a solid surface. I assume a shield is a solid surface, and you can open the cloth as required.
4. As far as RAW goes, it does not state that it is fixed - simply that it needs to be fixed to a solid object.
5. RAW leads me to believe that the the thickness of the shield has no bearing on the depth of the hole itself.

Answer 4

IF this were in my game, I would ask that the player hire someone that knows this kind of magic well to either make a hole of a particular shape and size as a custom item, and make them earn the result. Also, a hole of smaller size would be equally smaller internally. For example the RAW is a 6ft diameter 10ft deep. If they wanted a 2ft hole, it would be (2/6) x 10 feet deep. If they had a kite shield, it would be kite shaped and an approximately scaled hole depth.

As far as the edge is concerned, I agree that if damaged the hole would be considered broken and the contents would be trapped inside the pocket dimension unless they can break free, or the item is repaired by someone capable enough to make the item in the first place. I would also let my players find out the hard way that an attack could cut the edge and ruin their new toy if they don't specify a way of protecting it from being struck because I'm an evil bastard and I love making my players cringe... muahahahahaaaaa!

This would make for some SUPER interesting combat! The only reason I would allow this mechanic is because it can be broken free of with a DC 10 STR check as an action. The interior would certainly be an indestructible impenetrable extra-dimensional surface devoid of all properties acting only as a barrier. It would be clever to make it removable as well, maybe one portion of the border that would allow you to access the edge of the cloth so you can fold it. Otherwise, it would remain open all of the time and lose some of its functionality as a storage device.

https://roll20.net/compendium/dnd5e/Portable%20Hole#content