FINAL BOSS MOVE THAT NEGATES ALL BUFFS AND POSITIVE STATUS - FAIR OR NOT?

If your game is designed such that surviving until you set up all your buffs is 100% of the challenge in late-game boss fights, like Shin Megami Tensei games and Wild ARMs Alter Code F, this kind of dispel can definitely help make a boss fight more interesting. That kind of design often happens late in a game when the player has obtained a lot of different buff spells that stack with each-other, which makes the difference in power between a buffed and unbuffed party really high.

Sometimes the boss dispelling the player's buffs can force players to find other strategies besides just buffing until they're invincible. Other times it can force players to continue rebuffing themselves throughout the entire fight instead of just during the first part. Depending on your game balance, and depending on how often the boss uses its dispel (and whether or not it's an AOE dispel), either or both of these player strategies might be viable against a dispel boss. The boss's power will need to be reduced to compensate though.

I really like MOG's suggestion of a timed or conditional buff wipe. Make it very clear that if anybody has more than 3 status effects on them, the boss will get pissed and do the buff wipe.

You could also do a partial wipe -- like this move clears all attack buffs and this move clears all defense buffs. Put those on a rotating timer and the player gets some breathing room. Or, everybody could just randomly lose one buff or lose one stack.

All sorts of ways to play with it! It's highly variable based on your game, like others have said.

Ah yup, that sounds perfect! If it's something the player can work around or prevent, I think you're golden. It makes the player keep their interrupts ready or have to recover by rebuffing if they mess up.

Ways how I'd do it:

a) Have the game track how many buffs are up, and if it surpasses a certain number, the boss clears all your buffs, meaning you have to distribute your suddenly limited amount of buffs much more cleverly.

b) Make it a single-target attack, so you have to focus on keeping buffs up, while also encouraging the player to not just stack all the buffs on one character. Plus, if you have way to make the enemy target your tank-type characters more often, you can use that to keep the debuffing skill away from the guys that need it.

c) Some of the boss's attacks strip specific buffs away.

author=unity
In my game, there is a state called Charge where a boss spends a turn charging up a move, and the hero has TP skills that can cancel the charged state. Right now, I'm thinking, having the Mass Dispel a telegraphed charge, so you can see it coming and possibly break it and keep the last boss from dispelling everyone.

I enjoy using this kind of mechanic as well, although I usually don't have straight-up a "stop enemy charge" skill.

I usually force the player to look at their skills and go "ok, what is this attack likely to be, and how do I stop it", with solutions varying between using a stun, shredding their accuracy for that turn, "silencing/sealing" that ability with the right status effect, or just plain old "have everyone defend". That way the player gets to feel clever that "hon hon, I saw the Spider salivating from the mouth while charging up, so I silenced it to stop mouth-based skills, and now it can't spit the super-powerful poison attack at me. Hon hon, aren't I clever?"

...I don't know why I threw in a gratuitous french accent.

Didn't most Final Fantasy bosses have some kind of move which destroyed all of the team's enhancements? For example, Zeromus in Final Fantasy IV had "Black Hole". And I know that there were others.

Well, honestly as long as the player can build a strategy along it, so it makes the fight more interesting its a good idea. If its just arbitrary and random, then its more annoying. If stat buffs are inherently important throughout your game, and this is the only boss that does this, you basically just nerfed a key gameplay feature in your last fight, especially if the usage is arbitrary. If they weren't important, players won't even notice.

I can see two good ways of doing this, both of which are based on SMT-styled gameplay. A few bosses in SMT will cast that games version of mass unbuff (De-kaja), when you have a certain amount of buffs up. This forces players to limit how many buffs they can cast, but if the player is given some indication (A message in combat each time you buff, indicating how close you are to the ability), they can manage it by applying only very important buffs. Another set of bosses apply the removal spell if you have any buffs. This is important in how the battle encourages players to deal with it, since with the modern SMT systems bosses have quite a few turns per party set of turns, so either way it forces them to waste a turn removing party buffs. If the monster requires buffs to damage sufficiently, then you need to put up the buffs quickly and then blast the boss before they get removed. If they don't, you can have just one character throw up a buff to force the boss to waste a turn.