You do realize that's not how copyright works, right?
And that it's not related in the slightest to you stealing and building off his work?
The debate isn't about the legality of this, it's about the morality of it.
Not sourcing the sprites you work from (and, as surt showcased, the animations you trace) is a scummy move and may also count under plagiarism law, if you do want to get legal with it.
Stop trying to deflect, you did a bad thing. Apologize and don't do it in the future, dragging it out like this just makes you come off as incredibly disingenuous.
Pretty much. ^
The Wyvern was fan art- I never intended my pixel rendition of it to be used for profit.
It also is my art. I don't approve of you using it and passing it as your work.
Long version; I re-adapted this creature concept (3D, low poly) into pixel art form. Requiring substantial study to make it work in the FFT style, and be a perfect fit. A skill and capabilities demo in and of itself, if I had wanted to display it in my 2008 portfolio: "Look at my skills in creating a concept in this format. Do you like it, (possible future client)?"
"Here's the original concept, (client), so you can compare. It's from [game]." - Credit is important, so they know exactly what they're getting.
"Yes, I can turn your concepts into pixel art versions."
Similarly, your portfolio should be full of these clarifications and credit giving where credit is due, especially if your only role in the displayed work was to add animation frames. Or tracing from another 2D work. Or sprite recoloring/amalgamating.
Stealing and ripping are entirely different issues altogether.