How do multiple Sanctuary Vessel features (from the Genie Patron Warlock) interact together?

Question

For this scenario, there will be 2 level 20 Elven Genie Warlocks (to make it simple.)

Steps:

1. Both go inside elf 1's Sanctuary Vessel and stay there for 12 hours
2. Both go inside elf 2's Sanctuary Vessel while inside elf 1's, as the Genie Vessel is an object and does not get ejected from the first vessel, take a long rest there (4 hours for both,) and then wait for 8 hours. At the end of elf 2's Sanctuary Vessel, both are ejected into elf 1's.

My question is can elf 1 use their Sanctuary Vessel to stay in their Genie Vessel without having to completely exit both, or are both ejected out of Vessel 1 and can then re-enter it?

Answer 1

Ask your DM

As always in such corner cases, it may be useful to talk to your DM to understand if he is OK with something like this, and understand that, if this does create issues and unbalances play, your DM might decide to shut it down, RAW or not.

There is a reason why many other extradimensional spaces blow up if you put them inside each other: it curbs such shenanigans.

The Sanctuary Vessel does not have such language, so this would not be the case here. However, it has the following language:

As a bonus action, you can eject any number of creatures from the vessel, and everyone is ejected if you leave or die or if the vessel is destroyed.

So, it is not clear what will happen if your buddy warlock tries to take you into his vessel: will you both end up there, or will both be ejected?

By an optional rule in Xanathar's Guide to Everything (p. 77), if there are multiple simultaneous effects that stack at the same time caused by a player’s action, that player gets to decide the order in which they happen.

In rare cases, effects can happen at the same time, especially at the start or end of a creature's turn. If two or more things happen at the same time on a character or monster's turn, the person at the game table - whether player or DM - who controls that creature decides the order in which those things happen.

So here your buddy could decide that first you enter his vessel, then the ejection would happen — but at that point, you are not there anymore. Note that the rule is optional. You DM could also rule that you instead get ejected.

Reentering seems not to pose a challenge, as both of you took s long rest since you entered the vessel.

Once you enter the vessel, you can't enter again until you finish a long rest.

There may also be some fencepost timing questions, as you need to hit the time for moving to vessel 2 exactly right, and I’m not sure what method the character would have to measure time that exactly. Maybe there is a spell? In the real word, even the best mechanical chronometers can have several seconds of deviation in 24 hours.

So my impression is that from a technical rule perspective, this could work. And it may not cause issues in play either.

Given that you need two high-tier Genie Warlocks to make this possible, it’s likely not something that has too much practical relevance for actual play. Having two such similar characters in the same party would be unusual and pose interesting roleplaying challenges by itself.