Ghost

Ghost is a word game in which players take turns adding individual letters to a growing word fragment, trying not to be the one to complete a valid word. Each fragment must be the beginning of an actual word, and, for our purposes, we will consider 4 to be the minimum word length. The player who completes a word or creates a fragment that is not the prefix of a word loses the round.

So on player 1's turn, they can:

challenge player 2's word if they think player 2 has formed a valid word of at least 4 letters. If the fragment is a word, then player 1 wins; if the fragment is not a word, then player 2 wins.
challenge player 2's word if they think that no word can be formed with the current fragment. Then, player 2 must provide a valid word starting with the current fragment or lose.
add a letter to move the fragment towards a valid word
attempt to bluff player 2 by adding a letter that doesn't move the fragment towards a valid word