Many of the in-depth details used are from Undertale Wiki and the Deltarune Wiki.
Background
Undertale is a RPG and a Bullet Hell game developed and published by indie developer Toby Fox with the help of Temmie Chang.
In Undertale, The Player controls a human child who has climbed Mt. Ebott and fallen into the Underground: A large, place where monsters reside underneath the surface of the Earth separated by a magic barrier created by the humans. The Monsters living in the Underground were trapped there after a war against the humans. The game has 3 pathways Neutral(which contains multiple endings depending on who you spare/kill), True Pacifist, and Genocide, each depending on your actions throughout the game.
Explanations
Power of this Verse
Undertale's power level ranges a lot. The highest beings are Multiverse level. Where it strives in are the hax like Determination (Which allows the wielder to Time Travel upon death, power null lesser DT users, and a lot more), Time manipulation, Soul Manipulation, Essence Manipulation, Concept Manipulation, Psychokinesis, Bone Manipulation, Magic, and more.
Knowledgeable Members
Characters
Undertale
Others
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The Annoying Dog
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The Anomaly
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Asriel Dreemurr
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W. D. Gaster
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Flowey
Humans
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Frisk
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Chara
Monsters
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Asgore Dreemurr
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Sans
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Mettaton
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Muffet
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Undyne
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Papyrus
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Toriel
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Napstablook
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Snowdrake
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Loox
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Froggit
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Moldsmal
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Vegetoid
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Whimsun
Civilization
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Underground