"Dess" and "death" would be transcribed exactly the same in Japanese (デス), a language Toby Fox is very familiar with.
The following picture is from Tumblr. Very easy to interpret as about being dead.
Goner Kid's last lines are "Please forget about me. Please don't think about this anymore."
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Death is occasionally linked to freedom in Undertale.
Snippet of Gerson's dialogue when asked about the prophecy in the Neutral Route:
"Legend has it, an 'angel' who has seen the surface will descend from above and bring us freedom.
Lately, the people have been taking a bleaker outlook...
Callin' that winged circle the 'Angel of Death.'
A harbinger of destruction, waitin' to 'free' us from this mortal realm..."
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Snippet of Flowey's dialogue from the Genocide Route:
"There's just one thing left I want to do.
Let's finish what we started.
Let's free everyone.
Then... let's let them see what humanity is REALLY like!
That despite it all...
This world is still 'kill or be killed!!'"
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So far, the secret bosses in Deltarune all have a theme of being separated from the world. Jevil is imprisoned, and Spamton's friends have all abandoned him.
Snippet of Jevil's dialogue:
"I AM INNOCENT, INNOCENT. I JUST WANTED TO PLAY A GAME, GAME.
BUT THE BORING KINGS FOUND SUCH FUN TO BE A TROUBLE.
AS PUNISHMENT, THEY CRAVED TO IMPRISON MY BODY.
BUT I'M FAST, FAST, CLEVER, CLEVER.
THEY LOST THE CHASE, AND LOCKED UP THEIR ENTIRE RACE,
BUILDING A PRISON AROUND THE WHOLE WORLD. NOW I'M THE ONLY FREE ONE."
[Ralsei] "Huh? Free? But you're clearly the one behind bars..."
"THINGS DON'T SEEM SUCH FROM HERE, LIGHTNERS!"
[Susie] "Well, sounds like you don't need any help, then."
"THAT IS UN-SO. I GROW LONELY IN MY LITTLE FREEDOM.
SO, SHALL YOU PLAY A GAME WITH ME, ME...?
I'LL SHOW YOU WHAT IT MEANS TO BE FREE!"
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Snippet of Spamton's dialogue:
"HA HA HA ... THIS POWER IS
FREEDOM.
I WON'T HAVE TO BE JUST A PUPPET ANY MORE!!!!
...
OR... so... I... thought.
WHAT ARE THESE STRINGS!? WHY AM I NOT [BIG] ENOUGH!? It's still DARK... SO DARK!"
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