Parry is a game mechanic that requires the player(s) to press the jump button again while jumping, any pink object can be parried and usually, it will build up the super meter. It is also very useful to escape situations like the Big Wave attack from Sally Stageplay or the card attack from King Dice. The parry animation consists of Cuphead or Mugman turning the end of their straw into a hand which slaps the parryable object and becoming pink for a few frames. There are two upgrades that can be bought at Porkrind's Emporium that are related to parrying (Parry Sugar and Whetstone).
When Whetstone is equipped, parrying doubles as a weapon. When parrying now, instead of a hand appearing on the top of the straw, an axe appears instead. The axe deals 16 damage, but it is much slower and cannot be used rapidly, as it requires the player to land before they can use it again.
When Parry Sugar aka P.Sugar is equipped, the player will parry automatically once after jumping.