Long Reach is an ability that prevents the user from making contact with its target when using move that would usually cause physical contact. This ability is exclusive to Decidueye, an evolved form of the Grass/Ghost-type starter Pokémon from the Alola region, which was introduced in Generation VII (Pokémon Sun and Moon).
Non-Contact Moves: Normally, certain moves would require the user to physically touch the opponent, potentially triggering effects such as Static, Poison Point, or the activation of an item like a Rocky Helmet. Long Reach bypasses these on-contact effects, allowing Decidueye to safely use its moves without the risk of being afflicted by these harmful consequences.
Synergy with Moves: Long Reach can work in synergy with a variety of moves that would usually involve physical contact. For example, moves like Leaf Blade, Spirit Shackle, and Brave Bird become safer to use, as they will not trigger the aforementioned abilities and items