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During a combat that takes place on top of a moving vehicle (let's say a bus moving at 60 feet per round), What happens if you use the spell blink?

The blink spell description states that:

At the start of your next turn, and when the spell ends if you are on the Ethereal Plane, you return to an unoccupied space of your choice that you can see within 10 feet of the space you vanished from.

What reference plane would we use to determine "the space you vanished from"? Would it be:

  1. relative to the bus – in which case you'd reappear near the same spot on the bus, but 60 feet forward, due to the bus' motion?
  2. relative to the world at large – in which case you'd reappear 60 feet behind the bus?
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Rules As Written

There's no specific definition of "stationary" in the game. Depending on your point of view, nothing is stationary, because planets whip through the cosmos at thousands of miles per hour.

That said, I've seen it ruled both ways, because there are no hard rules either way. One of the core design tenets of 5th Edition is "rulings over rules". Some things are deliberately left to the GM's discretion.

Advice

Personally, my ruling it based on mapping: if it's big enough or elaborate enough that a battle can take place on it, then it's big enough to count as a stationary object for spells that require them (like teleportation circles onboard ships).

For some specific examples:

  • Boat - Nope, because boats aren't big enough to be a set piece on their own. Even large boats, like say a viking style longboat, don't count. They're potentially sizable, but they don't have multiple decks, compartments with doors, stairways and ladders, etc. I wouldn't bother mapping the details of that kind of boat, like I would a proper ship. To put it another way, during an encounter, boats will move around within the lakes or rivers the encounter takes place on, but a ship is where the encounter takes place.

  • Carriage - Nope, for the same reason. It's going to be part of an encounter, not a setting for the entire encounter.

  • Iceberg - Again, assuming it's large enough... yes. It's not specifically about dimensions, though - an iceberg just big enough for the spell's area wouldn't cut it. If it isn't big enough to be a setting for an encounter, if it isn't worth the time to draw out, it's not big enough to count as stationary.

To be clear, my ruling is not based on physical dimensions, beyond needing the minimum the spell calls for (10' radius for Tiny Hut, 10' diameter for Teleportation Circle, etc). It's about the importance of the area and the worthiness to be setting for an encounter.

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Keep the PC's Position Relative to the Battlefield

(which might be the bus top)

As is common: this is a DM call. Also, we have justification for either method. The rules say: "every location on (the prime material plane) has a corresponding location on the Ethereal Plane", so the top of the bus likely still exists in the ethereal.

According to previous canon, structures (like a bus) were usually represented as gray objects in the ethereal plane, which you could move through if desired, but you usually remained 'standing' on the (ghostly) floor that you were previously standing on (even though you might be standing on an object moving rapidly through space, like a planet)

However, this is probably more of a "frame of reference" issue, so it is also reasonable to view that the bus could continue without you (even if you were inside, since you can easily move through walls). Also, blink says "you return to an unoccupied space of your choice that you can see within 10 feet of the space you vanished from", which again seems to make it a frame of reference issue. It probably wouldn't be questioned if you were inside a floating castle, but the frame of reference on top of a moving bus is more subjective.

Ultimately, it's often best keep the PC's position relative to the battlefield similar to up-voted answers here:

So if the bus is moving around on a battlemap, it's probably not the battlefield. But if the bus is the battlemap, your players might have certain expectations.

For precedence, published adventures typically treat large moving environments the same as static environments (for the purpose of casting glyphs and such). But these are typically larger than a bus. Examples:

  • Rise of Tiamat has a moving iceberg dungeon that has glyphs
  • DDEP5-02: Ark of the Mountains is a Flying Ship that has glyphs in it
  • DDAL06-02 The Redemption of Kelvan has an earthmote with glyphs in it
  • Hoard of the Dragon Queen features a moving cloud castle with glyphs in it
  • Tomb of Annihilation has a moving earthmote that contains a permanent teleportation circle

Alternately, I might let the player make a skill roll (like Arcana) to decide for themselves.

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  • 2
    \$\begingroup\$ My concern is that, while you could probably ride the bus from the Etherial plane, blink explicitly says that you reappear in a space within 10ft of the space you vanished from. Would that space move with the bus? \$\endgroup\$ – divibisan May 24 at 17:13
  • \$\begingroup\$ FYI the immovable rod post rules using the ground and not the battlefield. They do leave it up to an Arcana check though \$\endgroup\$ – Weasemunk May 24 at 17:55
  • \$\begingroup\$ I'm not sure if I'd say that blink is innocuous. That's a spell that, when activates, safeguards the caster. Not every spell works in every situation, and this may be one where it doesn't. \$\endgroup\$ – NautArch May 24 at 18:29
  • \$\begingroup\$ Couple of things; the questions you link to as support don't really support, but most importantly, are you equating a bus to the size of a large ship? \$\endgroup\$ – NautArch May 29 at 17:35
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Your reference frame in the Ethereal should be the same as the Material

In dynamics, all motion occurs relative to a frame of reference, since motion is the act of things moving relative to each other. When you Blink, you must also have a frame of reference.

Your "relative to the world" example still picks a reference frame of the world. You could also potentially define your frame of reference relative to the plane you're on. If it's a constrained single-world plane, the two are equivalent, but if your plane has planets, you could find yourself off-world due to the motion of the planet.

We know that there are no cases that force you off-world, so the question is how to decide what your frame of reference should be. In the standard case, your frame defaults to world frame because your velocity is fixed relative to it. It makes sense that we would use the bus for your case because your velocity is fixed relative to it.

A description of the Ethereal Plane is as follows:

The Ethereal Plane is a misty, fog--bound dimension that is sometimes described as a great ocean. Its shores, called the Border Ethereal, overlap the Material Plane and the Inner Planes, so that every location on those planes has a corresponding location on the Ethereal Plane.

A description of Etherealness is as follows:

You ignore all Objects and Effects that aren't on the Ethereal Plane, allowing you to move through Objects you perceive on the plan you originated from.

It is apparent that you can move through objects on the Ethereal Plane, but you don't automatically do this, since you are not flung off-world, as discussed above. This adds credence to the theory that you keep whichever reference frame in which you are stationary at rest.

Unfortunately, there is no explicit RAW answer for you, but I believe any other answer has to make assumptions that are not RAW.

Ultimately, this is a DM ruling

Without a RAW answer, it is up to the DM to break ambiguities and decide how to set the reference frame. While I believe the above makes sense, your DM may decide otherwise, which is his/her prerogative. It is your right, however, to ask ahead of time how such a situation will be ruled and expect that ruling in all cases. Ask your DM to set a precedent or allow some player flexibility, such as using an Arcana check, as suggested by @MattVincent.

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  • \$\begingroup\$ @MattVincent Thanks! Do you have any reference for that? What stops you from falling through the planet? \$\endgroup\$ – Weasemunk May 24 at 18:08
  • \$\begingroup\$ Ah I see, so you could move into the planet if you chose to do so. I'll revamp the answer \$\endgroup\$ – Weasemunk May 24 at 18:14
  • \$\begingroup\$ Let us continue this discussion in chat. \$\endgroup\$ – Weasemunk May 24 at 18:20
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I disagree with the other answers and I think you stay on the bus and even supported by RAW. Let me explain.

I assume we can all agree that the 6 seconds of a round in dnd-5e are supposedly happening at the same time. However, as everyone moving at the same time would be a great chaos a round is split into turns. A necessary abstraction. A citation from the phb would be nice here but I don't have one at hand and I don't think anyone disagrees with this point.

Now in order to answer the question posed above, we need to remove this abstraction. This would mean that the player, which is using blink, is in the material plane during his turn which is the same time frame as the round. Also in this round, the bus moves at the same time as the player is in the material plane, so the player is moved with the bus.

Now you might wonder, if the player is in the material plane during the whole round, why can't enemy's attack him, because during their turn he is suddenly in the ethereal plane. By RAW this is simply a limitation of the abstraction of turns that we use.

However I even have a cinematic answer to this. Consider the xmen scene where nightcrawler attacks the White House. Especially in the room with the president, he is most of the time in the material plane and only teleporting a short distance. When he teleport he nearly immediately reappears in a different not to far away spot. And yet nobody hits him. Its not completely similar to blink as nightcrawler teleports probably a bit more than 10 feet and stays in the material world a bit less than 6 seconds, but that's just fair because blink is less powerful. if in dnd a player with blink would attack this many enemy's he would lose because they would ready their action and just kill him when he appears. (https://youtu.be/StnmzjqMKRo).

To sum up if nightcrawler would be on a bus and would be in contact to the bus each time he appears he would stay moving with the bus. So that is how I think the blink spell works by RAW.

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  • \$\begingroup\$ Why downvote but give no reason for it? \$\endgroup\$ – findusl Jul 8 at 13:31
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It is ultimately up to the DMs discretion

There are two possibilities for what can happen in this scenario, and both of them are reasonable based on all available official ruling:

  • Your point of reference is on the surface you cast the spell, and you re-enter the material plane atop the bus
  • Your point of reference is fixed to the environment surrounding the bus, and you re-enter from that position

Ideally before blinking in this situation, you would discuss your plan with your DM, and they could give some form of relatively easy skill check to determine whether you scuff your point of reference.

On another note however, when looking at combat from a purely rules-based perspective: RAW there is nothing capable of severely affecting your surroundings such that the world around you moves. Combat in the game wasn't designed with a moving environment in mind, and therefore spells are designed to function within a stationary one.

As I see it, this would be the best way to apply ruling to this situation, unless the player wishes otherwise:

Combat is taking place atop the bus, and the bus is stationary. The world is moving underneath it, and considered difficult terrain. Anything that ends its turn there will take damage and be swept 60ft away from the bus

Others have posted these links as well, but I'll link them again because of how similar they are to this one:

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  • \$\begingroup\$ @NautArch imo the DM shouldn't say "no" when a player wants to do something that isn't 100% according to the rules, and instead "yes, but". In this scenario I think the player could have good reason to want either thing to happen, but they shouldn't just be able to choose freely because as you said, there is a ruling against that. I'd probably say to them that if they don't want their frame of reference to be the bus, they'd need to make some form of check to accomplish it. \$\endgroup\$ – Whambulance May 24 at 19:18

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