All monsters are Pansexual by default.

In Undertale, Sans is older then Papyrus but in Underswap, Papyrus is the older one.

All the following ships are true: Grillby x Muffet, Papyrus x Mettaton, THE OG ( Alphys x Undyne ), Nice Cream Guy x BurgerPants

Frisk and Chara are Non-Binary

Papyrus is Aware of what Sans is Capable of and his "Time Shenanigans"

When these characters both died, Asriel is 13 years old and Chara was 10, making Asriel the Older sibling by 3 years.

Asgore still feels affection for Toriel but Toriel dislikes him

All the Souls were 13 years old when they died.

King Asgore only killed 3 souls, while the other souls died by other causes.

Gaster is indeed a skeleton

Gaster isn't alive.