What's the difference between the difficulty choices?

[Jxt09]

I've only played on Normal. What changes in Hard mode? Do the enemies make better choices? It gets annoying when the enemy sometimes doesn't choose to make a skull match or even a match 4, because I know the computer AI knows that match is there and that that's the best match to make but it decides not to to give the player a chance. It feels like the AI is condesending towards me.

[Duder]

I was wondering this myself. After fighting the same enemy several times on different difficulties it appears that their stats are exactly the same (including health points, spell resist, etc.) regardless of difficulty, at least in quick battle mode. If you weren't aware, you can mouse over the enemy portrait to see their stats.

I did some searching and on this discussion post [forums.penny-arcade.com] someone pasted a related question from an interview with one of the developers and I've bolded the relevant portion:

Автор сообщения: some interview

Interviewer: Some PQ players are adamant that the AI "cheats" by knowing what pieces will fall from the top of the board. We've found these falls benefit the player as often as the AI, but some owners are insistent. Can you confirm/deny, and possibly walk us through the AI's decision-making process when it examines potential matches?

Dev: The AI definitely does NOT cheat. I actually scripted all the AI for the game, so I am 100% certain it doesn't cheat, and as I mentioned in a post on our Forums, I'm far too lazy to make the it cheat anyway - if I'd wanted to make the game harder I would have just given the enemies more Life Points!
The AI has a very simple decision-making process... it looks around the board at all available moves and gives each one a score between 0-100 based only on what it would give immediately (it doesn't look ahead at all). It then looks at all its available spells and gives each one a score between 0-100 based on how useful they would be. Finally it picks the move with the best score. On "Hard" difficulty it always picks the best one, On "Normal" it picks one of the top 10%, and on "Easy" it picks one of the top 50%.
One interesting thing the AI does is to bias its scores slightly higher towards the bottom of the board, because matching lower down tends to give more possibilities for cascades.

Unless someone else has more information, it seems difficulty only changes the likelihood of the enemy to select the best move.

[Jxt09]

Great. Thanks for finding that. I think I'll try it on hard mode from now on. And that also explains why sometimes the prompt tells me to make a move that I can see will be stupid because it will line up some skulls for the enemy to match on his next move. I tend to only rely on the prompt to see if there's a four of a kind match that I'm missing, other than that I make up my own mind what to match next.

[Duder]

Yea, it is probably best not to go by the prompt unless it points out a four in a row move. It doesn't tell you what move is best, it just points out a move that is available to you.