Regular vs. Challenge Games
Difference Between The Formats
In a Regular game, all words formed in a turn are validated against the selected word-list prior to being placed on the board.
In the Challenge format, words are placed on the board without validation. Here is a scenario of Player A vs B where A has just played a turn and B has challenged:
Words formed were valid - Player B has lost the challenge, it is now Player A's turn.
Words were invalid - Player B has win the challenge. Player A's last play is removed from the board and score is adjusted. Player B continues the game.
You can currently play Challenge games only via the desktop.
Starting A Challenge Game