B for Vengeance. Despite it's situational use, it's very handy. Though I do a lot of postgame spotpass battles with my bro and others so take it for what it's worth haha.
A for Tomebreaker. Since magic gets used more as the game closes, this is a great skill to have. Plus I like envisioning my character grabbing the opponent's tome and breaking it's spine before slamming it onto the ground. --- "If you level up a Swellow at night then give it a Dusk Stone [they didn't exist yet] then it will evolve into Ostricho." ~ The Legend of Ostricho