My character is in a sack and being carried by an Echo Knight fighter who teleports using the bonus action from Manifest Echo:
You can use the echo in the following ways:
- As a bonus action, you can teleport, magically swapping places with your echo at a cost of 15 feet of your movement, regardless of the distance between the two of you.
Do I come with them with all their stuff or stay at the spot where they teleported from?
Oddly enough, "teleport" is not a rules term. There are no general rules tied to 'teleport' that tell us how to expect it to work. Usually we would say "then you default to the English meaning of the word", but that only tells us that teleporting means movement between two places without crossing the distance between them; it doesn't tell us anything about how teleportation interacts with objects and creatures in the game world.
Now, the Sage Advice Compendium does say this:
Misty step doesn’t say the caster can bring worn or carried equipment with them. Are they intended to leave everything, including their clothes, behind?
No, the caster’s worn and carried equipment are intended to go with them.
Some teleportation effects do specify that you teleport with your gear; such specification is an example of a rule being needlessly fastidious, since no teleportation effect in the game assumes that you teleport without your clothes, just as the general movement rules don’t assume that you drop everything when you walk
Your equipment goes with you even if the ability doesn't say so. Still, a carried creature isn't equipment, and it doesn't say other creatures can come with you when "you" teleport. Teleportation abilities that are intended to bring creatures with you always say so explicitly.
But on the other hand, if I have an ability that says "you move" or "you fly", I would certainly expect that such movement would include bringing along another creature that I'm carrying. And since there are no special rules for teleportation, we don't have a strong reason to think teleporting is different from walking in terms of what you can bring along with you.
Ultimately there's no clear answer to this. There's no strong argument against bringing other creatures along with a teleportation effect like this, except that some teleportation methods specifically allow you to bring a friend, implying that there's an unspoken limitation. And being required to carry somebody to bring them with you does impose a limitation that isn't present for teleportation abilities that let you do it with a touch, or just by being nearby.
Since the rules aren't very clear, it's up to your DM to make this call. That's an unsatisfying answer, but it's the only one we can really give here.
If it were my table, I'd probably rule that the swap only brings your actual equipment with you, and not creatures that you happen to be carrying, whether that's a cat or a half-orc. I certainly don't want to encourage the players to abuse the ability -- one of the limiting factors of the echo knight swap is that you or your echo has to have already physically reached the place you're swapping to (unless it's within 15 feet, where you can manifest the echo and immediately swap for a very short range teleport effect). You can more or less be in two places at once, but it doesn't really let you reach locations you couldn't otherwise get to. As soon as you can bring other people with you, that goes out the window and this becomes a very powerful ability that's available at will, so I'm inclined to disallow it. If one interpretation has no serious ill effects on the game and the other is potentially game-breaking, I'm going with the safer option!
Even though the teleport ability of the Manifest Echo does not say so explicitly, the Sage Advice Compendium has explicitly ruled that equipment worn or carried is taken along during teleportation:
Misty step doesn’t say the caster can bring worn or carried equipment with them. Are they intended to leave everything, including their clothes, behind?
No, the caster’s worn and carried equipment are intended to go with them.
Some teleportation effects do specify that you teleport with your gear; such specification is an example of a rule being needlessly fastidious, since no teleportation effect in the game assumes that you teleport without your clothes, just as the general movement rules don’t assume that you drop everything when you walk.
Teleportation effects that allow you to transport additional creatures say so, such as the Teleport spell:
This spell instantly transports you and up to eight willing creatures of your choice that you can see within range, [...]
Manifest Echo by itself only teleports you and your equipment. However, here the situation is somewhat different: the passenger creature is not another creature standing next to you, that you can elect to also teleport without extra effort. You have lifted up this creature and are carrying it around, it is not independent of you. The question then is if you can consider a carried creature to be part of your equipment?
The main argument for this comes from the Variant Encumbrance rules on p. 176 of the PHB:
The rules for lifting and carrying are intentionally simple. Here is a variant if you are looking for more detailed rules for determining how a character is hindered by the weight of equipment.
While the rule itself is optional, it treats anything that the character is lifting or carrying as "equipment": the total weight of what you carry is what determines penalties to movement, and this total is referred to here as the "weight of equipment". If creatures you carry would not count against the "weight of equipment", they would not slow your movement speed.
Now, it's possible (even likely) that the writers of the PHB did not think of carrying a creature when they used the term equipment here, because you normally do not carry creatures around, and they instead should have referred to "the weight of everything the character carries."
A secondary argument is that if a character had a small cage with a live canary in their equipment (to detect poison gas in dungeons early), would you rule the canary is left behind when they teleport because as a creature it cannot count towards their equipment?1 I wouldn't, but like a PC, the canary is a creature.
First, when game terms are not defined we use the common English definition of the term, and for equipment or gear that is:
the set of articles or physical resources serving to equip a person or thing: such as (1): the implements used in an operation or activity
which does not sound as if this should include persons. Normally, when you think of equipment, you think of objects you carry around.
Second, the question of the canary falls more into the territory of how to treat harmless, diminutive creatures, namely that one likely best ignores their being creatures in most cases.
Third, the reason why teleporting is limited to an individual or defined number of creatures, is game balance. Taking a PC along with you, wether in a bag or on your shoulder, is a lot more powerful than having a canary in your backpack. Allowing a character to take along a fellow PC by lifting them up temporarily so they become "equipment" is a bit of cheating, it creates a loophole and circumvents the restriction that you can only teleport yourself.
Allowing this would significantly increase the power of these spells and abilities.
I think overall characters are not intended to count as equipment, and hence you will not be able to teleport with a carried creature.
If the DM prefer the rule of cool, and wants to allow heroic shenanigans, like the wizard nearly breaking down to put the barbarian over their shoulder to teleport away with them, or like here, the Echo Knight bagging a fellow character, they can rule otherwise.
1 If you rule that the canary is left behind, Misty Step is a great way to get rid of lice, tapeworms, fleas, and other parasites.
