editing sources to art that I know of that are taken here in this comment

the source for the design above is here

other undertale designs up on this shop

another sans shirt original source of this sans art

papyrus shirt original source of this papyrus art

Update: I did report the situation to Toby Fox through Tumblr, and did contact ichibangravity about his art being taken so far, will try to inform more of the original artists of their work being taken