Delta Stream

Delta Stream is the signature ability of Mega Rayquaza that fundamentally alters the battlefield by creating a mysterious air current weather condition. When Mega Rayquaza enters battle, this unique weather effect immediately activates, providing a powerful defensive boost by neutralizing all super effective attacks against Flying-type Pokémon. Any move that would normally deal double damage to Flying types instead deals neutral damage, effectively removing the type's traditional weaknesses to Electric, Ice, and Rock attacks.

What makes Delta Stream particularly potent in competitive play is its weather-locking properties. Unlike standard weather conditions, the mysterious air current cannot be overridden by typical weather-changing moves or abilities, with only Desolate Land and Primordial Sea capable of replacing it. This creates an incredibly stable defensive environment that persists as long as Mega Rayquaza remains on the field. Abilities like Air Lock and Cloud Nine can suppress the Flying-type protection but cannot change the weather itself, maintaining the lock.

The ability's impact extends beyond just Mega Rayquaza, as any Flying-type Pokémon on the field benefits from the immunity to super effective damage. However, it's worth noting that certain effects like Stealth Rock and the Anticipation ability are specifically unaffected by Delta Stream, maintaining their normal interactions with Flying types. This creates a unique metagame dynamic where Mega Rayquaza can safely switch in against traditionally threatening Electric and Ice attacks while providing team support.