7 x 7 grid of letters generated randomly based upon the frequency of letters in the ~180K word dictionary.
Randomly selected letters begin to fade away with an increasing probability based on the level.
Rate of fading also increases at higher levels.
Fading letters are contagious, which results in new letters tending to begin fading adjacent to already fading letters.
If a completely faded letter is at the bottom of a column when a word is made, the entire column will fall out. This limits the ability to make words.
Missing columns can be replaced which will deduct points from your score.
Letters can also be replaced individually with the Trade button, again deducting points.
All letters, except fading ones, can be replaced with the Scramble button.
Occasionally, bonus words of 7 or more letters are presented for you to find. Bonus words have a higher point value than if the word were found during normal game play.