I have indeed thought about unlockables (skins, powerups and color themes) via a system of achievements.
What if you fused the in-sight/out of sight idea with your item idea? Instead of rewarding the sight concept with straight-up points, it could fill up a special meter. Once the meter reaches certain points, you could spend your acquired “MP”(meter points) to activate one of 3-4 “items” or skills in your arsenal (if you waned to make the game even more in-depth, you could add pseudo-RPG elements, where a player’s built-up scores from many past games could be used to buy new, slightly more potent skills).
Your idea is very interesting, although it's missing a few elements. Who is getting meter points when pacman is being seen? All cats? Only the cats in range? That would only encourage plainly following Pacman to rack up MP. Plus, why would you need items when you're very close to catching pacman?
I had an idea while studying yours though.
What if the cats who can currently see the mouse got points, increasing every consecutive second (up to a cap, to make it not too profitable to plainly follow the mouse), while the other ones would rack up MP, based on how far they are and to help them catch up? When the bar is full, they would get an item (like you said).
Obviously, when no cat sees the mouse, no points nor MP are awarded).
The cats would have to choose between chasing the mouse head on, or waiting and striking at the right moment.
The AI controlled cats (when there's less than 3 cat players) would obviously follow the mouse blindly (to put pressure on the player)
Meanwhile, the mouse could receive MP for every second it is hidden, and when its meter is full, an additionnal power pellet could appear for him to use.
Do you guys think that's a good idea?
I was also thinking of a quicktime event, but I wouldn't know where or when to trigger these events.
I don't know about this. I don't want the cats to feel penalized for using items, especially if the effect is game changing (like destroying walls). I feel like the powerups should be rewarded on good plays and the cats should feel good using them.
You could give the cats a score bonus at the start of the round and deduct points when they collect/use power-ups. This way the player (cat) that uses no power ups to catch the mouse will get more points for catching than the player that needed help.
I really appreciate your insight, keep those ideas coming!