Taleland

When talking about the meaning of the dress in this instance it's important to recognize that the dress can't be separated from the mannequin, both contextually and literally.

They are a package deal. The dress is permanently attached to the mannequin and must be analyzed with this context in mind. The dress being unobtainable on its own and instead being affixed to the mannequin makes this item inherently different from the dress in Undertale.

In Undertale, the dress is wearable. It's free to be given or taken with nothing to get in the way of that. In Deltarune, the mannequin flips this aspect of freedom on its head. The dress is unable to be taken off the mannequin or given to anyone else. The choice is taken away and the object is rendered useless.

The mannequin represents a lack of choice in the ill-fitting roles imposed upon oneself by others, and I think chapter 5 bolsters this idea even more with Pink's comment about how it "doesn't fit" just like how Spamton won't fit into the mannequin in chapter 2. Conversely, Ralsei likes the dress, but would be unable to wear it because it is instead being forced onto someone who doesn't want it.

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