Can I only use the trick of the top card?
Even when I draw 3 cards?
Yes, you can only use the (regular) trick of the Top Card. I do believe there is a trick that says you can use any trick of your top three cards.
And I think you can any Magic Trick (if it's in your top three)
If one of your top 3 cards has a Magic Trick then you
can choose the Magic Trick as your Trick. If you do this
then you must ‘Play’ that card this round.