Two truths, one lie was a game played between at least two players. At the start, one player would say three statements, two of which were true and one was false. The other player would then try to figure out which statements were true and which one was the lie.
The Sixth Doctor managed to trick the Toymaker by playing a game of two truths, one lie, where he gave three statements (1. The Doctor is one of the Toymaker's toys. 2. The Doctor is not the Toymaker's puppet, so he must go free. 3. The Toymaker has the Doctor in a trap that is designed to place him under his control.) These statements left the Toymaker unable to answer as if he guessed correctly, the Doctor would have the truth and claim victory, and if he guessed incorrectly, he would lose the game. (PROSE: Trick or Treat)