The eternal cave

Throughout the multiverse are entrances to a truly enormous cave that spans them all: The Eternal Cave. Time spent within it is tracked by a hand-sized device referred to as a compass, despite not tracking orientation, and one appears for each resident after their first day. Upon entering, a resident starts at A, and every day, the letter shifts by one, becoming B, C, and so on. After reaching Z, the timer changes to AA, and when ZZ is reached, AAA follows. No known resident has reached a four-letter time, leading to rumors that something happens after ZZZ, the most popular one being that the resident will be granted a wish. Only the most determined beings of the multiverse enter the cave, as the whole process takes 18,279 days to complete - Just over 50 years. Thankfully, most bodily functions seem to be suspended in some way while in the cave, and even aging does not occur, but the wait is still excruciatingly long to such a degree that no one is known to have finished it.
The Eternal Cave's dangers extend beyond sheer boredom, however. At seemingly random times, its layout will shift, altering the great many paths and chambers within. While the change itself has not been known to harm anyone, a path will rarely be entirely closed off, forcing whatever residents may be inside to find another, or wait and hope it reopens. Flooded sections also exist, and unfortunately, the usage of oxygen is one of the few biological processes not stopped while in the cave, leading to incidents of drowning. 
The cave's greatest threat, which has fortunately long since passed, was a colossal monstrosity nearly 30 feet across, with dozens of arms instead of legs. It was lured into a similarly enormous well, and its grip on the walls broken, causing it to plummet deep within. The well had no known bottom, even after being checked by residents capable of flight, leading to it being the perfect place to dispose of the creature, as it seemed to be unbeatable in a straight fight. Since then, the older residents have warned others to stay clear of the well, just in case the monster somehow survived and plans on returning.
As the cave's entrance can be found in every universe, its residents are odd at the best of times, and humans are an exceedingly rare sight. Despite its ubiquitous entrances, the cave cannot be used to move between universes; any residents who leave are simply returned to their own. All language in the cave is automatically translated to whatever one the listener is most comfortable with, a fact that all residents greatly appreciate, as the other languages likely don't even exist in their own universe. Residents typically do not give out their names, instead being given nicknames by other residents. Below are the descriptions of 4 of them.

"Inverse Samurai", a 2-foot tall being, seemingly human, with blue armor and a sword of blue energy, which they rarely sheathe. For whatever reason, gravity is reversed on them, and they walk on the ceiling instead of the floor. Their time in the cave is UE.
"Rogue", a monkey capable of speech. Known to enjoy stealing things from other residents, including their compasses. Occasionally a group bands together to retrieve their belongings, and while they always succeed, Rogue simply continues their theft. Their time in the cave is BL.
"Squire", a 1'6 anthropomorphic dragon. Some people saw their scales as blue, and others as purple. Some time ago, they joined a group looking to explore a flooded area, and came across an enormous dragon statue within. The statue had its mouth open with a tunnel leading inside, and Squire went in to see what might be there. Shortly after, the statue's mouth snapped shut, (presumably) trapping him inside. He hasn't been seen since, and is assumed to have drowned. His time was QE at the time, though if he remains alive somehow, his time in the cave is SP.
"Elder", a 20-foot tall winged blue dragon with six legs. Had been in the cave far longer than any current resident, and was involved with dropping the arm monster down the well. If she'd come for a wish, she never told anyone what it was. Was in the same exploration group as Squire, and investigated the same statue. One of her wings was caught in the statue's mouth, and couldn't be freed in time, leading to her drowning. Her final time was ZAH.