The Istari's Magic.......and other beings?

[lathspell]

but could elves in some cases?

Yes, most elves new about magic, yet some of course were more powerful and had the greater knowledge about it. Because of them using magic, they do not know that the 'mortal word' magic means. Remember Galadriel in LotR - FotR, when she asks Frodo and Sam to see her mirror, saying something like: 'You wished to see magic, didn't you? Well, now you can see magic, I think, for I do not know what the word means.'

This will not be the exact words, but it is the same meaning.
So yes, most elves could do magic.

. And Beren did too, did he transform into Draugluin or something else? Oh well, but besides Beren and Luthien, and the Istari, were there any other beings that possessed some magic?

Beren did indeed change into the form of Draugluin (this is, I believe, when they are going to Thangorodrim, after Sauron is overthrown and Draugluin is slain by Huán), but it wasn't him who did that. I don't believe that he knew magic. It was with the aid of Luthien Tinuviel that he gained that form, it was 'her magic'.

Yes, there were some other elves that could do magic, Galadriel and such. Maybe there were men too, I dunno, maybe the men of Nümenorë.

greetings,
lathspell