May I play six Gandalfs if three are from the Core Set and three from the Hobbit? 'Cause they have same name although being different cards…

No, you can only have 3 cards with the same title, by official rules.

Gandalf from Core and Hobbit share the same title, so you can only have 3 cards in one deck.

See page 27 of the core rules:

"A tournament deck must contain a minimum of 50 cards. Additionally, no more than three copies of any card, by title , can be included in a player’s deck."

OK thanks. That's annoying. It would have made great possibilities.

Eladamri, Seed of Freyalise said:

But nothing prevents you from using 1/2 Gandalf (Core) and 2/1 Gandalf (Hobbit)….