what does gear 2 do mechanically?

[Grimbus]

does it just raise attack?

[WzRd]

Activates Gear 2 increasing your attack stat. Last for 5 turns, also believing it activates with Luffy using his Gear 2 skills. Not necessarily needed to use before using Gear 2 skills although useful to use say your down on TP, you can activate for the damage boost as you build your TP.