Patch 6.0.2 (2014-10-14): Now learned at level 38 (was 20) and redesigned.
Feral: Your autoattacks have a chance to reduce the Energy cost of your next Cat Form ability by 100%.
Restoration: Your periodic healing from Lifebloom has a 4% chance to cause you to enter a Clearcasting state, causing your next Regrowth to be free.
Old: Your autoattacks have a small chance and your periodic healing from Lifebloom has a 4% chance to cause you to enter a Clearcasting state. The Clearcasting state reduces the Mana, Rage or Energy cost of your next cast-time damaging or healing spell or offensive feral ability by 100%. Does not affect Nourish.
Patch 5.1.0 (2012-11-27): Now has a different visual effect for Feral Druids.
Patch 5.0.4 (2012-08-28): Now a Feral and Restoration specialization passive ability. Restoration version now has a 4% chance to trigger from Lifebloom periodic healing, and does not affect Nourish.
Patch 4.2.0 (2011-06-28): Clearcasting buff from now lasts 15 seconds, up from 8 seconds.
Patch 4.0.6 (2011-02-08): Can no longer trigger from helpful spells (aka heals), unless the Restoration talent [Malfurion's Gift] is chosen.
Patch 4.0.1 (2010-10-12): Now available to all druids at level 20 (was a tier 3 Restoration talent).
Patch 3.0.3 (2008-11-04): Will no longer be triggered by the Honorless Target buff gained when entering the world.
Patch 3.0.2 (2008-10-14): Now a passive ability, triggering from damage spells, healing spells, and auto attacks.
Old: Imbues the Druid with natural energy. Each of the Druid's melee attacks has a chance of causing the caster to enter a Clearcasting state. The Clearcasting state reduces the Mana, Rage or Energy cost of your next damage or healing spell or offensive ability by 100%. Lasts 30 min.
Special attacks will no longer consume their own clearcasting state. All melee attacks will now be able to trigger the clearcasting state.
This spell now works correctly with [Bash], [Rip], [Ferocious Bite], and [Demoralizing Roar], granting a decrease in the cost of the ability. Ferocious Bite will still use the entire energy bar to generate additional damage.
Patch 1.8.0 (2005-10-10): Now a buff instead of a weapon enhancement, and can proc off of all melee attacks. Clearcasting now affects all abilities instead of just spells.