None taken, but I think people know where the pokemon come from, and not necessarily where the art you see in the pokemon games comes from. If you want to create your own pokemon sprite, you wouldn't need to give credit; however, this is copied pixel-for-pixel from pokemon diamond & pearl, so credit to the original artist should be given.
There's no point repeating yourself on the internet. If I want to see what you wrote for a second time, I can just scroll up. Allow me to rephrase my reply: The artist should either create their own pixel art or give credit to the original artist. Let me use an analogy. If I were to quote an author word-for-word in my writing, I'd need to give credit to them and use quotation marks. On the other hand, I could paraphrase and wouldn't need to quote or credit.
Even if it's obvious that I'm quoting a famous author's work, it's still considered plagiarism if I don't use quotation marks. Just like it is considered plagiarism if I were to copy someone's art without giving credit.
Paraphrasing, in this case, would be creating pixel art of a pokemon that already exists and quoting would be copying the original pixel art pixel-for-pixel.
Let me repeat myself again. People are probably more than capable of knowing exactly where this guy got these sprite images from. In fact I don't think I've ever seen a bead sprite on the front page that wasn't some copy from a game. Also, your analogy sucks. Writing is not at all the same thing as visual art when it comes to outside influences. There are millions of people on the internet who come up with creative ways to recreate something like the Mona Lisa with beads or paper bits or other random objects, but I don't see anybody complaining that they didn't type up a whole bibliography in MLA format just to say so. On the reverse side, I've read plenty of books where the author referenced a contemporary event or product without crediting anybody. It's because everybody knows what it is and nobody cares if the author takes an extra paragraph to explain it. And regarding that last bit, I'd say creating pixel art of something that already exists would be more along the lines of simply referencing something. Recreating the image entirely in a completely different medium would be the art equivalent to paraphrasing if you absolutely must compare it. Quoting would be if the guy had simply created pixel art on a computer using a bunch of sprites that somebody else put together, and only then would it constitute the need for extensive crediting. Besides, the image here isn't even identical to the original. I don't know if you noticed this, but Haunter doesn't have any yellow bits in the game.
Long story short: Creating a replica of a famous image from scratch in an entirely new medium has absolutely nothing to do with literature and does not require all this fuss over credit.