UNDOCUMENTED MECHANICS
Costs 1 durability when it triggers — this skill wears your weapon down.
"Chance of losing durability", "Slows Enemies" above follow a diminishing curve, not a flat gain per level; the other numbers in the same block do not: "Chance of losing durability": 46% at level 1, 35% at 5, 30% at 10, 25% at 20, 20% at the limit; "Slows Enemies": 11% at level 1, 37% at 5, 51% at 10, 63% at 20, 75% at the limit. Reaching the limit takes skill level 60, gear bonuses included, so the first few points are worth far more than the last ones.