Defense is the most important thing you can learn to do in a fighting game. With a solid defensive mentality and skillset, you are going to be better than average at pretty much any fighting game. However, in complicated fighting games like Guilty Gear, there are some specific defensive options that are very important to know about. The following is an attempt to explain what most advanced players know about Instant Blocking and Faultless Defense, and how each are used.
Basically, in order to understand how to apply FD and IB, you have to have a strong idea of what they actually do.
- Blocks chip damage
- Causes the defender to take MORE blockstun
- Costs a small amount of meter
- Increases pushback for the attacker
- Cancels whatever you're doing instantly (IF you can FD)
- Can block air-unblockable moves
- Causes the defender to take LESS blockstun
- Improves your meter gain slightly
- Decreases pushback for the attacker
Core Usage: Escaping/Punishing Pressure
The most important use of FD/IB is creating holes in the opponent's pressure. To do this well, you have to know about the opponent's character: What are they doing right now? What can they do from it? Is the string they're doing solid, or is it part of a false gap mixup? How much stun is each individual move putting you in? How much pushback is each individual move doing?
With this in mind, you can start trying to get out of pressure in a few key situations. Most of the time, your opponent needs two things to keep you locked down: They need to be close enough to hit with an attack, and they need to be able to do another attack before or shortly after you're out of blockstun. With this in mind, try to think of situations where your opponent needs to connect in order to continue their pressure. This is true of most normal moves, since they need to connect to cancel to the next thing, but is often not true if the next thing they're going to do is move to close the gap (With a run, jump, or airdash, or with some special move that carries them forward) or throw a projectile. Places where your opponent needs to connect to continue their pressure are places where they can screw up.
Next, you need to identify which of these critical points are vulnerable to IBing or FDing. If a string of attacks will barely be close enough to connect, you can FD a single hit, or sometimes a few hits, leading up to that critical point, forcing them further away, and if you were smart about it, causing them to whiff (Or, against a smarter opponent, just stop attacking before they'd whiff). On the other hand, sometimes a string of attacks will have a point that barely keeps you in blockstun. If a string or a link almost lets you out of blockstun, but doesn't, or lets you out of blockstun, but not long enough to do something, it's a good time to instant block. This allows you some time to reversal, backdash, or even jump out sometimes. Often, an instant block will allow you to throw your opponent, because not only are you in less blockstun, but you are closer to your opponent than they expected you to be.
Being able to identify these situations comes with experience, and often differs greatly between individual characters you'll be facing. It never hurts to go into training mode and try out a string you're having trouble getting out of. See where it's vulnerable, and what you can do to break out of it. What move in the string do you want to interrupt, or avoid? What move should you be looking for to FD/IB?
Alternate Use for FD: Cancelling Movement
Since FD causes you to block immediately, it can be used to cancel a number of things. The most specifically useful ones are jump startup and run animation.
One Frame Jump: Jumping takes a few frames (3 for most characters, more for some) to get off the ground, during which you're fully vulnerable. If you FD during your jump, you will jump slightly faster (There's some controversy over exactly how many frames this gains you). This is useful not only for jumping more safely, but for getting off the ground quicker, and works with superjumps as well as normal jumps.
Dash cancel: For every run in the game, there's a short "sliding" animation that plays when you stop running. During this time, you can cancel into any attack, but you're completely unable to block or throw. But, if you FD while running or sliding, it will cancel it instantly, and allow you to do either. Note that airdashes cannot be cancelled by FD (But they can be cancelled by Slashback)
Animation cancel: Any ground normal, as well as most characters' j.Ds, can be cancelled into FD on the first 2 or so frames. This is usually pretty much entirely useless in most cases. However, you can sometimes psych out an opponent with the sound of an attack you don't end up doing (Audible overheads, for example). Cancelling j.D is also a way to option select airthrows into FD if you don't have burst (By pressing 4H+D and then instantly FDing, you get the throw if in range, and D->FD if you aren't.). This is a lot of effort for fairly limited utility, however.
Situational Uses for FD and IB when you can't escape
When you're pretty sure you're going to be unable to escape pressure, there are still uses for FD and IB. You probably already know that FD cancels chip damage, and IB will gain you meter faster (While also allowing you to improve your familiarity with the rhythm of your opponent's strings).
Another weird use of FD is cancelling the animation of a failed slashback. For reasons I'm not quite sure of myself, holding FD with, for example, K+S, and tapping H will allow you to attempt more slashbacks in the same amount of time than you'd be able to otherwise. This is pretty much only useful in theory, since anyone with the execution to do it reliably in a way that's useful could probably just time the slashback in the first place. But, you know, kinda cool.