The Wild Card booster unlocks at Level 11. It can be used as any of the 26 letters ... just like a blank tile in "Scrabble". The game's dictionary will automatically assign it a letter, if possible, to turn the letters into your letter rack into a valid word.
When you use a Wild Card, it immediately goes to the next open slot in your letter tray.
Note that sometimes Wild Cards will appear naturally, for free, among the cards on your board or in your draw pile.
Wild Cards are worth 0 points; however, they can be valuable scoring-wise by increasing the word-length multiplier.
If you are curious what letter the game "thinks" your Wild Card is, tap the Dictionary Definition button when you have a valid word in your letter tray that includes a Wild Card. Currently, there is no way to change the letter that the game picks for your Wild Card ... but we're working on it!
HISTORICAL NOTE: Wild Cards were first invented by Euston T. Wild, an unsuccessful cattle rancher and moderately successful bank robber, in the Wyoming territory during the 1870's.
HYSTERICAL NOTE: All Historical Notes are vetted for accuracy by our research partners at Glibbitz, Glibbitz, Glibbitz & Noid.