GPL violation in Tomba! Special Edition?

It's important to point out that the concept of "linking" is not mentioned in the GPL's definition of "Program" or "covered work", nor is it used as a determiner to decide if the viral nature applies to your work or not. That's a common misconception that people who've read about GPL but never read the actual license text have. I point that out here only because the developer here mentioned it, but it's irrelevant.

The viral nature applies if you "convey a work based on the Program, or the modifications to produce it from the Program" unless it is "a compilation of a covered work with other separate and independent works, which are not by their nature extensions of the covered work, and which are not combined with it such as to form a larger program" [0].

If that sounds vague enough to be interpreted in a lot of different ways to you, you're right. Even the FSF themselves admit it would be up to a court to decide[1] (which unfortunately in a lot of cases means whoever has the most money wins).

tl;dr - When in doubt, assume you need to make your work GPL too.

[0]: https://www.gnu.org/licenses/gpl-3.0.en.html

[1]: https://www.gnu.org/licenses/gpl-faq.html#MereAggregation