Frisk is called Faint (Froussard in Original Version).
Chara is called Luigi.
Papyrus is the leader of the royal guard.
Undyne is dead and is most ferocious when Alphys brought her back to life
Asgore is dead.
Flowey is the king of Underground.
Many monsters are most carefull about Faint.
Many peoples from another dimensions (like Error Sans, Ink, Frankenstein and Mr.Resetti) appear.
Gaster appear to help the player during the battle against Omega Mufffet.
Muffet attack Faint instead of Flowey when the human arrives at ruins.
Toriel don't help Faint.
Sans capture Faint and takes him at his house
Grillby attack Faint at the end of Snowdin.
Monster Kid doesn't follow Faint in Waterfall.
Papyrus attack Faint at the place of Undyne.
Just after the battle against Papyrus, Undyne attack Faint.
After Faint met Alphys, Temmie move the Tem Shop to the cave of Muffet.
Flowey fight the human instead of Asgore and use five of the six humans soul one by one.
Muffet take the last soul (the perseverance soul) before Flowey and beat him, absorbs the five other humans souls and become Omega Muffet.