So as we all know the original Mysterio has been back since the Gauntlet story arc and has been a member of the current Sinister Six. The thing that really confuses me is that Mysterio said he had faked his death, which does not make sense with his previous appearance.
Back during Civil War, when Spiderman revealed his identity, a new Mysterio(Klum) decided to attack Peter Parker at the high school he worked at. The second Mysterio(Berkhart) decided to team up with Spiderman to take down Klum. If you think having two Mysterio's around at the same is confusing, then this part will really blow your mind. So Klum and Berkhart were both confronted by the spirit of the original Mysterio(Beck). Eventually Klum was injured by Eros and he has never been seen since. The same goes for Berkhart.
Some could make the argument that Beck was trying to scare the other two away from the mantle and waited for the right time to strike(much like Hobgoblin). He is he master of illusions so he could easily use some tech to make it look like he was a ghost. Well the thing is he was dying of lung cancer and had a brain tumor, which is why the police let him out of prison early. I honestly can not think of a logical explanation for how he survived that, especially if it was terminal. It is unlikely that this some illusion or something, since he did not have any of his equipment with him in his cell.
I do feel Mysterio's death was very much like Kraven's(he even killed himself like Kraven). Mysterio was dying and this was his "last hunt". I know that Mysterio's death was not as dramatic as Kraven's, but him not actually dying takes something away from the character. Its like what if during Grim Hunt Kraven says "I never actually died, it was a trick!"
Maybe they brought him back because of the Gauntlet story arc and maybe even Ends of the Earth, but there are still two Mysterious around. They could have replaced Beck with Klum or Berkhart(just like they did with Vulture). Heck they could of had Beck stay as a "ghost". Hopefully there is some explanation for this is in the future like that the current Mysterio is actually Klum.