When a player plays an action card can they choose to play the card for just the amber value in the top left hand corner or does the player have to execute the action as well. For example when playing lost in the woods can the player choose to just collect the amber at the top or do you have to shuffle two creatures per side into their controllers deck.

Thanks!

you must carry out as much as you possibly can, and skip that you cannot (e.g. opponent has no creatures,. you have 2 - you must shuffle in your 2). this includes playing upgrades on opponent's cards, or healing them, for example.

As the above poster said, you must carry out as much of the action as possible unless the card says “may”.