What other mythical beasts or characters could they add to the series?

I don't see Beth adding anymore, but bringing back creatures is a possibility

Creatures from Solstheim would be nice.

Can you please elaborate on what klind of creatures these are?

Minotaurs, centaurs (variations like skeletons centaurs, orc centaurs), gryphons and sea serpents (considering you can attack while swimming or on a boat) would be cool.

Things I'd like to see:

Banshees
Werebears
Wendigos
Wraiths
Will-O-The-Wisps
Harpies (possibly younger Hag Ravens?)
Hydras or sea serpents in the Sea of Ghosts
Chimeras might be interesting
Cyclopes could be a variant of giants

There's probably more I could think of if pressed, but that'll do for now.

Dragons, because real dragons have four legs, not two.