Thank you very much eishiya!
I will ask the original creator for permission then, and I'll remove if s/he don't want me to use his/her work, otherwise I'll update the description.
Pluffers from deviantArt made the originals. This particular artwork of theirs has been stolen a lot. They're okay with people reposting it as long as it's credited, but I don't know how okay they are with tracings/redrawings of it. It's best to ask first!
In general, for any artwork, if you don't have permission from the original artist or don't even know who the original artist is, it's best not to post anything that uses that artwork. Making a reference to it is fine (e.g. if you drew different Pokesirs as a nod to the original ones, since the new artwork is entirely your own), but if you're using it directly (including it in yours with or without modifications, tracing it, etc), the polite thing to do is to get permission. If you're not making money from your version, you're not breaking any laws by posting it so there's nothing that can really stop you, but many artists like to know what people are doing with their art and like to have some measure of control over their art.
Hmm, this got me an ideaaaaaaa!