Sample
Knock Off:
(Dark-type)
65 BP - removes item and if successful adds 50% more damage
Since its introduction in the ADV Era, Knock Off niche before was getting rid of the held items of the opposing Pokemon which is always threatening but the problem was that it is a 20 BP move and the those that can use it were better off using other moves offensively or defensively. In Gen. 6, the Pokemon God have graciously changed this into a devastating move. The first was its BP have increased to a somewhat respectable 65 BP . the second was the nerf to steel-types defensively, allowing dark- and ghost-type moves to hit for neutral damage, and lastly the buff it's secondary effect was the icing on the cake. Not only did it retain the item removal effect but also if it does remove an item successfully it gets an additional 50% damage meaning it is a 97.5 BP move (not counting STAB) used on a 'mon with a held item while also removing it.
It's wide distribution and great utility also helped to make it into a fearsome move today. From giving Fighting-types a way to super effectively damage psychics that can would wall it. To crippling those that heavily relies on items defensively or offensively. It also gave dark-types a another decent physical STAB choice than Sucker Punch/Night Slash/Crunch. An example is Crawdaunt, due to Adaptability and a high 120 Atk stat can make use of Knock Off to devastating effects.
It's not always rainbow and butterflies here because this move is not without drawbacks. One is since it has 65 BP it can be a poor choice of attack when used on someone without an item already or holds a mega stone, especially on those that resists it. Second is there are still 'mons who can take even a STAB Knock Off and in return KO the user or cripple it for the rest of the match.
But whatever cons this move has, the amount of utility it offers is something that all players will surely want to have in their arsenal in today's metagame.
Defog
(Flying-type)
Lowers evasion by one stage. Also removes sticky web, stealth rock, spikes, toxic spikes, safeguard, mist on all player's side of the field while only removing reflect and light screen on the target's side.
If you look at this move since the time it was created, one may think of its niche of removing reflects and light screens, an effect which is outclassed by brick break, while also lowering the target's evasion by one stage but if one take a look more closely, it will also remove all hazards that is on the target's side making all your hazards that you set-up go to waste. And then comes Pokemon XY which , much like Knock Off, the pokemon God also decided to make this into a more useful move.
This move was changed so that now it removes all hazards on both sides on the field, while retaining it's others effect, making it act like a rapid spin but instead cannot be blocked by Ghost-types. It now allowed more pokemons that learns defog to be used differently
