Multiscale

Multiscale halves all damage the Pokemon receives when its HP is completely full, introduced in Generation V. This effective 50% damage reduction applies to all sources of direct damage regardless of type, making the first hit against a full-HP Multiscale user significantly less threatening.

The reduction only applies while HP is at 100% -- even 1 point of prior damage from entry hazards, weather, or any other source will disable it entirely. This makes Multiscale users extremely vulnerable to Stealth Rock, Spikes, and other chip damage that breaks the threshold before the opponent can attack. Conversely, moves like Roost allow the user to restore full HP and reactivate the ability repeatedly.

Multiscale is found on only 2 Pokemon: Dragonite and its pre-evolution Dragonair (as a Hidden Ability). For Dragonite, Multiscale is arguably its defining competitive feature -- it guarantees survival of virtually any single unboosted hit, enabling setup with Dragon Dance or safe pivoting with Roost. The combination of Multiscale, Roost, and Dragonite's solid bulk creates one of the most reliable setup sweepers in the franchise. Heavy-Duty Boots to avoid Stealth Rock chip has become a staple item choice specifically to preserve Multiscale.