They have a dream to see their idol in action, hence The Idoliser.
“A list of characters that have the idoliser role. This is Monster Kid's role in Undertale.The Idoliser role list
“"Yo! You're a kid, too, right? I can tell'cause your shirt is striped!" – Grillby...Grillby/Storywarp
“"Yo! You're a kid too, right? I can tell'cause you're wearing a striped shirt." – Talking to...Monster Kid/FaxsTale