So I just hit me the other day, when a game offers a parry mechanic in a single player game from the ones I've played that offer it, the mechanic becomes overpowered fast and makes the game much easier then it by all means should be.
DMC 3 - 4
Offers a entire style rank up as a reword for pulling it off and unlike other moves in these games doesn't scale down how much style it builds with repeated use, a DT guage and builds it's own meter for one of the potentially most powerful attacks in the game and there is no exception to what it beats, even an attack the game expects you to dodge because it's a 1 hit kill can be parried and then use the meter it builds to 50% damage the boss when you get the chance.
Bayonetta. (Transformars devastation I guess too)
As simple as flicking the analog at the enemy, no negative for being off with your timing but heavily rewarded for it being well timed, get a strong counter attack + witch time + witch energy (Autobot super attack) meter gain and like before nothing in the game > this ability.
MGR:R
Here there is only 2 exceptions to moves that beat it here being 1 enemy made with an unblockable and by definition unparryable and the final boss who still does damage when blocked and parried (not that you should use the block input in this fight since another move bypasses his entire moveset.) Upon getting the timed block for parry it almost always one shots the enemy and on the last difficulty it can one shot some bosses due to both you and enemies having ridiculous damage.
Onimusha series
Parrying here is a 1 shot kill not for only the enemy but any enemy close the the parried enemy, but then they also reward the player for using this mechanic with 3X the orbs you'd usually get meaning with this you could gain access to much better equipment faster especially in the first where you have to level not only the swords but keys for access to other areas, it can also be done on bosses to make very, very fast work of them.
Dark Souls
Is it around your size? No need to put any effort in then just parry it and deal massive damage and walk behind for a quick back stab if it dared get back up, this is probobly the least overpowered as it doesn't work on things much bigger then you but it can still make short work of things that are.
What I'm getting at here is in Player vs Enemy it's not like playing someone else where a parry would be like some out read out played move, vs an AI opponent it's like you know exactly when they'll attack because they're made to attack like that and then and over rewarding for mechanics like that when they're not that hard, when vs an AI it should be a matter of seeing it once before you should be able to parry it every time from now on.
There are other examples I have but they fall in the same camp as above, are there any games that are player vs enemy AI that offers a parry mechanic that is not broken?