|“||Emergency! A meteor is coming! Smack it back into space with your bat!”|
|— Tutorial • Kirby Star Allies|
Star Slam Heroes plays similarly to Megaton Punch and Crackity Hack. The objective is to complete a series of action commands to allow the player's Kirby to smack an incoming meteor back into space with a baseball bat. Whichever player can bat the meteor the farthest distance wins. As it is slammed back, the meteor will crash through numerous moons and asteroids, signifying how far it has traveled. If the player fails to hit the meteor, it will crash into them, resulting in a distance of zero light years.
There are three difficulties: Town Crisis, Country Crisis, and World Crisis. Town Crisis is available from the beginning, and the player must complete Town Crisis to unlock the other two modes. In each difficulty setting, the player must charge up their bat a certain number of times, then time their swing to connect with the meteor. Town Crisis only allows the player to charge up once, while Country Crisis allows three times and World Crisis allows five times. Each instance of charging up takes the form of a power meter that goes up and down at a constant rate. The player must stop the meter as close to the top as possible to receive maximum charge; a successful charge is indicated by the fact that the bat is engulfed in increasingly-intense red flames. The player can take as much time as they like on each power meter, but since every mode only allows a period of five seconds to charge up before the meteor strikes, they must balance accuracy with speed. Once that period of five seconds is up, the player must swing at the moment when the meteor crosses their circular reticle to swing with maximum effect. Once launched, the meteor will travel a certain distance before being destroyed. The distance the meteor has traveled, in light years, is the player's score, and each of the four players' scores is compared to determine the winner.
Star Slam Heroes supports both traditional button controls and Joy-Con motion controls. When playing with a single Joy-Con, a button is still used to stop the meters, but the player must swing the controller to mimic the swing of the bat. However, the input is read the same as if a button was pressed.
- The music that plays during this sub-game is a remix of the music that plays on Nebula Belt from Kirby Air Ride.
- If the player achieves the maximum possible distance in any of the three difficulty levels (or a distance very close to the maximum), the meteor will smash into a UFO.
- Kirby's backwards baseball hat in this sub-game is a reference to the hat Ness, the protagonist of EarthBound, wears; this is because Ness's signature weapon is a baseball bat. Kirby's hat in this sub-game also resembles his Yo-Yo hat, albeit with a red coloration rather than a purple one.