- The yellow flowers found throughout Undertale are thought to be gorse, which bloom nearly all year round. They are also are sticky and used in salads and teas, traits mentioned in Undertale. Gorse is also a component in alternative medicine to restore hope and determination to those fallen into despair and hopelessness. An aid to regaining willpower and faith in times of strife.
- Chara means "darling, beloved, loved one" (Latin cārus), "joy" (Greek), and "Friend" (Irish). Chara is also the name of a star (Beta Canum Venaticorum) in the constellation Canes Venatici, that represents hunting dogs. It is the second-brightest star in the constellation. Along with the brighter star Cor Caroli, the pair form the "southern dog" in this constellation.
- Frisk means "lively, merry, playful" (Old French), "greedy, fierce" (Proto-Indo-European), or to search for hidden items, especially dangerous ones (German). It is also one of many Swedish army names originally given to soldiers to make their names more distinctive.
- Toriel and Asgore may be based on the irish púca, creatures with dark or white fur that take the form of goats, horses, cats, dogs, and hares. They are considered to be bringers both of good and bad fortune. There are stories of some púca being blood-thirsty beings, hunting down and killing their victims. Other stories portray them as benevolent or protective entities, intervening before a terrible accident or before a person happens upon a malevolent fairy or spirit. Human encounters with púca tend to occur in rural, isolated places, far from settlements or homes.
"You're surging with Bravery.
You've served Justice.
You're touched by Kindness.
You hold on to Patience.
You've upheld your Integrity.
You're braced with Perseverance.
You're filled with Determination."