Stencyl-tale: A Undertale Engine made in Stencyl.

[Kosheh]

Ton actually has a pretty solid point though in all seriousness. Though in my opinion, I'd shoot more for an engine that's Definitely Not Undertale and doesn't make itself look particularly obvious. Like...mash together Earthbound and Undertale, and make a mashup engine that still retains the schmup battle mechanic that allows you to either Kill Shit or Humorously Talk To Bad Guys - but make sure it doesn't feel 1:1 like Undertale.  It'd be interesting to have a Simple Alternative RPG maker that's putting-on-pants easy especially for curious game developers but I wouldn't explicitly push the feature of "Hey, you can make Undertale clones with it"

Like, basically...move all the menu options (like make it a square you operate with button keypresses) ship it with a different text box and a totally different font face and give the illusion that it could be an custom Undertale maker with heavy editing - but don't enable that from the get-go.

tl;dr you should make it a little more original, or you're gonna have a bad time

EDIT: Actually wait a second didn't the developer of Stencyl regularly post on PT long long ago? Have things really come full circle here?