how many battles did you do? it might have been random, but i have noticed this to. i think when your arena deck is being played it draws the cards that would make a good first hand. 8)
name of card : seeker monster card, costs 5 1/3 pay 3 to take one pillar from your deck and put it onto the field if anyone has anything to say about this card, let me know!
when upgraded turns into : massive seeker costs 4 0/4 pay 4 take a spell or pillar from your deck and add it to your hand if anyone has anything to say about this card, let me know!