The Fadecrest Sparrow was notorious for the practically impossible feat of landing a hit on it without also having a contract of the space attribute.
Rather, even for individuals with the space attribute, there was no guarantee that they'd be able to land a strong blow on it.
It has the annoying tendency to phase in and out of reality whenever an attack approaches it. Therefore all attacks, no matter the attribute, won't be able to land on it. Only an attack strong enough to destroy the area of space it had taken refuge in would be capable of harming it. However, space-attribute creatures strong enough to do so were typically only those in the higher levels.
Not to mention its ability to phase in and out of space makes most defensive measures against it useless. How can Aegis block it from attacking Kain when it can just phase through him at any point?