#senderverse background

So!

Because the original Undertale crew broke their Barrier and came to their Surface world first - a world that remembered monsters and magic in fairytales, and that treats monsters as their own sovereign nation with its own laws and culture - that particular magical metaphysical Barrier weakened significantly across the multiverse.

Because in the og Undertale, the Underground was actually in its own pocket dimension.

With me so far?

No?

Aweeesomeeeeee...

Continuing!

Since that particular Barrier weakened first, all the other Undergrounds break through that Barrier in particular.

So a few years after Undertale broke through their Barrier and appeared on the Surface, Underswap broke through the same Barrier.

Cue the confusion of the century in that Surface world lol.

Eventually, Underfell also broke through that Barrier. Then Horrortale. Then Swapfell. Then Fellswap. Then finally Lusttale.

They're still waiting on more Undergrounds breaking through, and they now have a whole set of laws and protocols to follow in case of another Surfacing.

Every new alternate universe that Surfaces gets sponsored by monsters from already-present universes. Monsters from particularly volatile or strange universes are monitored a little more closely, but there haven't been many unexpected incidents.

And finally, on to your question of why all my skeles have new names.

The long and short of it is because it's fair.

When Underswap broke through the Barrier, they weren't expecting to meet more monsters. They certainly weren't expecting to meet alternate versions of themselves, all with the same names as their own.

So after a long series of talks and discussions about identity and the importance of welcoming all monsters equally, everyone decided to discuss with their alternates what their names should be.

Some Underswap monsters didn't mind changing their names. Some Undertale monsters felt the same. Some monsters really wanted to keep their names, and went with a "Grillby the First" and "Grillby the Second" option. Some altered just a bit of their names, and some chose entirely new ones, and some based them on nicknames they already had, or traits they liked or valued in themselves.

And then, when Underfell broke through their Barrier another few years later, Undertale and Underswap monsters were already expecting a new group of monsters to come through. They'd been paying attention to the remnants of the Barrier. They had a welcoming committee ready, with laws and customs to be explained.

And then each group of three met up and worked together to figure out the newcomers' names.

The more new universes emerge, the smoother the process goes.

It helps a lot that the more volatile alternates are emerging into the UT Surface, where they can finally relax.