Opening Gambit gives the user Run Speed Up and Swim Speed Up (and in Splatoon 2, Ink Resistance Up) for the first 30 seconds of the battle. In Splatoon 2, that time is extended by 7.5 seconds for each splat and assist the user gets while the ability is still active.
This ability is restricted to headgear as a main ability, and cannot be rolled as a sub ability.
The ability is ideal for reaching objectives before opponents during the start of the match, gaining a tactical advantage.
Mutual exclusivity
This ability is found as the main ability only on headgear, so other abilities found only on headgear are mutually exclusive with it; in other words, players cannot have them together. These abilities are Comeback, Last-Ditch Effort, and Tenacity.
The ability is active for about 30 seconds starting from the start of a match. While the ability is active, that amount of time is extended by about 7.5 seconds for each splat and assist the user is credited with.