While few characters can have Unblockable attacks that are hard to predict (e.g. Nightmare's Stomping, Taki's Fury Ninja Cannon) they often suffer from being much weaker than most Unblockable attacks. This is likely done to balance their unpredictability, difficulty to dodge, or the combo abilities of these attacks. On rare occasions, characters can have powerful Unblockable attacks that are still fast and hard to dodge, such as Yoshimitsu and Setsuka.
Night Terror is often considered a very difficult NPC opponent due to his large arsenal of quick-execution, high-range Unblockable attacks (which are strangely unaffected by Guard Impacts).
Ivy possess two 'hidden' unblockables meaning that she can perform them without flames emerging from her blade or the screen darkening. Her SW (Sword State) A+B [A+B] is one of them, the other being SW 3B+K [3B+K]. Be careful of Ivy players using this. This may be a glitch or may have been intended in Ivy's design.
In Soulcalibur V, Just Guards can be used to block one of these attacks while Guard Impact does not have any effect. Brave Edge attacks occasionally involve an Unblockable attack. Unlike most Unblockables, they merely indicate that the Brave Edge is successful. If the Brave Edge attack is blocked successfully, it will end at the Guard Break part of the combo and the Unblockable will not be performed.