Dyna Blade is a boss fight in Kirby Super Star that appears in Dyna Blade and The Arena. She is a large bird that has a hitbox which consists of only her head.
Speedrun Route
Jet
When the fight starts, hover up to the top of the screen. Dyna Blade has a 50% chance to appear on either side, so you will want to stay in the middle to account for either side. Once she appears on screen, you will want to start holding Y to charge Jet, while pressing Left and Right back and forth so you are guaranteed to get a hit in. Once you are aware of the side, you can stay the opposite way so you hit her a second time with the Jet Burner.
To defeat Dyna Blade quickly, you will want to grab the stars that she emits once she lands on the ground. These stars not only have a specific hitbox, but have a short time window, making them fairly difficult to grab consistently.
Below are the positions you will want to aim for when grabbing the stars. You can use the bottom HUD as a reference for where to stand.