I love your design aesthetic, so I hope you don’t feel like I’m trying to nitpick on your shirt, but rather offer my opinion in a hopefully constructive way. For an Ugly Christmas Sweater, I think the “n’est pas” joke is unneeded. Jack Skellington stands on his own in a Christmas setting quite well. The broken ornaments are a nice touch. It would be more fitting the Ugly Sweater look to have some more horizontal knitting-type borders between your horizontal lines of decoration, even if you break those lines around Jack. Rather than Jack being in front of the horizontal elements, so some are showing half of a skull, just pause the line and restart it on the other side. Like how you did to Jack’s beard.
My last thought I’m not really sure how to articulate. Because I really like how you used a range of colors to transition and give things shape and shading. But I almost feel like you used it too much? Like for example in the skulls and candycanes, the darker shading that softens the shape of them, or the 2 (3?) colors of gray in the beard. But it’s making fun of a knitted shirt, so I don’t think those softened shapes are needed. Or the odd grays where Jack’s beard breaks for the text, it’s got some bumps that just don’t seem needed, a straight line would have been simpler and cleaner.
I’m loving the shape of Jack’s head and expression, you captured that so well. And I keep coming back to those broken ornaments!
I love Jack Skellington. I hope this one prints, so I’ll have another Nightmare Before Christmas shirt for my collection!