Pex is a Scrabble word

SmartFeud - the best word game ever

SmartFeud, a brand new game that is reminiscent of familiar board games, but is better, funnier, more exciting and more difficult.

The first thing you notice is that the board is bigger. 16 * 16 instead of 15 * 15. That may be a small difference, but in practice it gives you the little extra space you need.
But more importantly, with SmartFeud you can take a letter off the board every move to use for a word of your own.
Assuming your opponent bets "HAIL", you can now remove the "H" from the board and replace it with an "N" so that it is "NAIL".
For example, to put the word "NEAR", since you have to use the letter that you took off the board this move.
The only condition is that all the words on the board are in the dictionary and that you have to use the letter that you took off the board that move.
This additional option has major consequences. Each round you need to carefully consider which letter is suitable to take and whether you can use that letter. You are not required to take a letter off the board, but it can help.
For example, bonus boxes can also be reused by taking the correct letter off the board. That makes SmartFeud exciting until the end!