Trio Racquet

Trio Racquet is the first available Trio Attack for Paper Mario in Mario & Luigi: Paper Jam. After the brothers collect all Paper Toads for the first time outside the castle, the Paper Toads create a folded giant hammer for Trio Attack, and a Toad delivers that to the bros in which Paper Mario gains this option to battle enemies. It costs 6 BP.

When the attack is initiated, a wall appears and sticks the enemies to it. Luigi takes out a black ball and serves it with the button. The trio must then use their corresponding button ( for Mario, for Luigi, and  for Paper Mario) to hit the ball. They then rally the ball against the wall, damaging the enemies in the process. The ball increases in speed the longer the brothers rally the ball, and the attack ends when a brother misses the ball at a pivotal moment, or misses twice altogether. After seven hits, the ball lobs toward either Mario or Paper Mario, while also increasing in speed and size. The attack ends in two different ways: if Mario gets the final hit, he spins and strikes the ball with his racquet. If Paper Mario gets the final hit, he folds himself into a Japanese paper fan and hits it.

Striking three, five, seven and ten times with the squash will yield an "OK!", "Good!", "Great!" and "Excellent!" rating respectively.

Triva
This is the only trio attack that isn't initiated with the button