Multiplier Cards are want you want to see when you need mucho points.

There are two types of Multiplier Cards. 2x cards have a pink stripe, and double your score for any valid word that contains the 2x card. This is on top of the normal multiplier for word length.

3x cards have a blue stripe, and (I can see you are way ahead of me here) triples your score for any valid word, on top of the normal word length multiplier.

You can also combine Multiplier Cards in a single word for really astronomical scores. For example, if you had two 2x cards and one 3x cards in a single word, it would multiply the value of that word by 7x (2 + 2 + 3).