Hence his name, the Scissors is basically a giant, sentient pair of green scissors.
During the battle, the Scissors possesses two basic attacks. His first attack has him use his blades to shove Paper Mario away, and for his second attack, he will perform the Safe Tee, using his handles as a Golf Club. His primary gimmick is that Paper Mario has to time his attacks with the Scissors's movements. Basically, he has to hit Scissors's handle, which means attacking when Scissors puts his blades (which have the cover) in the air if Paper Mario uses his hammer, and on the ground if Paper Mario uses jump attacks.
After you knock his health bar below half, Scissors enters his second phase, which involves him shedding the covers on his blades. He will then charge up his next attack, which can break through your guard and cause an OHKO, though it can be dodged by jumping. Paper Mario has to find a way to freeze the boss with an ice vellumental, then swing the block around to damage him, then follow with a 1,000-Fold Arms Rush Attack. Defeating Scissors fixes up those who got cut up. The Scissors has around 400 hit points.