Uja will appear out of nowhere as a cloud of gray/black substance, pause shortly to assume a form, and start moving towards Kirby. Uja has a predetermined form depending on where it is found in the game.
It can transform into a shadowy hand or into a shadowy sword. If it is in hand form, it will grab Kirby, turn into a black oval, then float away, causing damage. If it is in sword form, it will come near Kirby and stab him with the tip, causing damage as well. Uja gives no ability when inhaled. It has high health, and so often requires multiple hits to be defeated. If it tries to attack Kirby, Kirby can avoid this simply by crouching down and wait for Uja to fly off.
- In hand form, the arrangement and behavior of Uja's fingers make it resemble Master Hand.
- Its similarity to Master Hand and its ability to change into a sword makes it resemble the Master Core, the final boss of Super Smash Bros. for Nintendo 3DS and Wii U.
- On June 13, 2016, the Arcade Bunny in Nintendo Badge Arcade mistook the two characters, referring to Uja as Master Hand.
- It only appears five times throughout the game — three times as a hand and twice as a sword.
- When possessed by Ghost Kirby, Uja is able to attack in all four directions.