Just making a quick note to myself.
MMORPGs which feature PvP usually have a problem with snares, stuns, fear, etc. On the one hand side you want characters to be able to do some of these things to make the game more interesting. On the other hand, chaining these things on another players creates a bad experience for him.
Now, you could ignore this problem if PvP was more about the grand scale, like strategy, than about the immediate fight. But generally it doesn't hurt to make the immediate fight in and on itself as fun as possible, too.
The classic solution are diminishing returns. If a stun/snare/fear/etc. is cast on a player who has suffered from a similar ability a bit earlier, it's less powerful. Eventually the victim becomes immune for some time.
Unfortunately this is a very straight-in-your-face mechanic and as such not very immersive. (Copying R. Kosters terminology here. I could just as well say that it doesn't make much sense from a simulation point of view and its only justification is the abstract gameplay.)
So here's the idea: Instead of diminishing returns, the ability to execute a stun/snare/fear/etc. is a proc which allows you to active the ability. You can't use the ability without the proc.
The chance of the proc can depend on many things, like the ability just used before. But it also depends on whether the victim has suffered a similar debuff recently. This makes for almost the same abstract gameplay as it allows developers to add such abilities to the game. But it is a much less in-your-face mechanic that makes a bit more sense from a simulation PoV.
If the proc stays for some amount of time and is not used immediately, it might even be possible to create playing styles (e.g. classes) which depend on such procs.