The boomerang gets activated each time you get a 3 card streak. Say your board has K-Q-J-J. You draw an ACE and proceed with K-Q, hit the boomerang and get the first J, which will then be removed and show the Q again, allowing you to get the other J card. Also, if you accidentlly hit the boomerang, you can undo it.
As for Goldie, it may help in the beginning to get rid of obstacles, if any, after that it’s just the boomerang and no holding our Goldie like before.