Mat Nastos is a semi-familiar face on the comic con circuit. As a writer and artist, he's had a few comic book stories published, including by DC Comics, with variant covers for IDW and Boom Comics, but he has mostly worked a sketch card artist for years. He's stopped now, still takes private commissions and appears at the odd show or two. Such as Salt Lake Comicon (his listing has now been removed) ….
And you can see him being interviewed about his work, here.
He's eBay listings say similar,
This is a ONE OF A KIND piece of original art on a rare and highly collectible blank sketch variant comic cover, done by a veteran comic book creator and film/tv writer/director, Mat Nastos. Mat Has worked on projects for Marvel, DC, Image, Disney, the SyFy Channel, Cinemax and is best known for his work on ElfQuest for Warp Graphics, Brigade for Image, and Phineas & Ferb for Disney.
The problem is… he never worked at Phineas & Ferb. As a sketch card artist, maybe he did a few images for someone licensed to do so, but that's hardly the same. And write the show? Never. And the creator of the show noticed.
He asks that "If you are part of the animation, comic, art community, I would appreciate your help to try to stop this fraud from continuing. If you become aware of this person making any claims about his relationship to or involvement with Phineas and Ferb or Dan and I, please let us know so we can pass it on the be dealt with through proper legal channels."
Mat Nastos did not reply to enquiries made. He has, however, removed the credit from his Facebook page…
Consider this a lesson for those who fluff their CVs or allow others to propagate such fluffing. Eventually someone notices. And working on sketch cards does not mean working on the property itself….