A 33% bonus to it can be found on the unique Razortail Belt as well.

Piercing is a property found on numerous unique bows and crossbows, usually set to 100%. The greatest to/hit possible in Diablo II is 95%, under any circumstances. It means that the target’s defense is set to zero, so your odds of hitting are greatly increased, but since your character’s level is factored against the target’s level, the actual to/hit will depend on how that formula plays out. The name is somewhat misleading, since it does not mean you will always hit the target. Ignores Target Defense is found on various Unique items and can also be added to a weapon by socketing the Jah rune. Click to the individual extra links below each section to read more in-depth information on each modifier. Some descriptions on this page are only basic information on the modifier. On Crafted Items the Clvl can be pre-set, but is usually determined by the random mods (since they’re usually higher than the minimum preset value).

These modifiers do not have Clvl requirements or Ilvls, as prefixes and suffixes do, and the character level required to use these items will always be pre-determined on Uniques and Set Items. There aren’t multiple types or levels of Crushing Blow, or ITD it’s either present or not to a preset value. These bonuses are picked from a pre-set list, not randomly-generated, and not randomly valued either. They are not like other prefixes or suffixes. Diablo 2 Special modifiers are bonuses found on such items as uniques, runewords, and Set Items, but not on magical or rare items.

Diablo 2 wiki rune list