i know that no one but Allah alone knows the unseen. So if someone asks me how the shaytan might look like on the day of resurrection and I answer that he will look wretched am i committing blasphemy by claiming to know the unseen? I hope for an urgent reply!
You should know that all of the unseen is for Allah and he knows all the things that are seen or unseen; a Muslim accords to Qur'an in all things. If Muslims say that Shaytan seems bad or prophets seem well in resurrection day, that is accorded to the Qur'an, so you should increase your studying of Qur'an. If we say that Feroun will go to hell, it is accorded to the Qur'an.