King Boom Boo is the fourth Boss of Hero Story, and is fought with Knuckles. The boss is separated into three phases: Approaching the hourglass, digging Boom Boo out of the ground, and delivering the four hits to kill him.
To approach the hourglass, the player should run directly down against the outer wall whilst Boom Boo throws his first two fireballs. After the second fireball, the player can turn inwards and start running towards the hourglass. The small ghost will trigger and run away if you get close enough and establish a line of sight to it before Boom Boo breathes in to charge his flame breath, which has a distinct audio cue. As soon as the breath sound plays, the ghost will no longer trigger. Pace can be determined by the timer when the camera switches to the view of the ceiling panel sliding open, at which point the player should aim to be sub-20.
The second phase is digging Boom Boo out of the ground, and is best performed by using Knuckles' quick acceleration movement strats; perform a short jump and glide to start moving quickly, then punch after you land on the ground to accelerate to maximum running speed. Do not atttempt to punch too early, otherwise you'll drill dive into the ground and waste time. As soon as you are on top of Boom Boo's shadow, he'll freeze in place and allow you to dig him out.
The third phase is delivering the four hits necessary to kill him, and should typically be performed in one cycle. After digging him out of the ground, perform the same fast accel strat with a jump/glide/ground punch, and deliver the first hit as you reach him. From here, the player should maintain an up-left angle on the control stick and time extra hits after his invulnerability runs out, which is 5 red flashes after he touches down on the ground. If your angle is too sharp to the left, you will run too far ahead of him and a punch will turn him around, losing the one-cycle, and if your angle is too sharp upwards, you won't catch up to him and will lose speed when you miss a punch, also losing the one-cycle.
If at any point you lose the one-cycle, it is recommended to restart, as it is faster than finishing a two-cycle fight, by approximately 15 seconds. If you are not confident in getting a one-cycle and aim to get a two-cycle fight, it is best done by getting one hit on the first cycle, and three hits on the second cycle. This is because Boom Boo's attack cycles change depending on his remaining health; after 2 hits, he will perform his chomping attack when he starts his attack cycle, which wastes time, and his fireball cycle also changes depending on how many hits are remaining;
4/3 hits: 4 fireballs
2 hits: 6 fireballs
1 hit: 8 fireballs
Moreover, the ghost trigger during the flame breath attack changes if Boom Boo has taken damage, and you will need to wait until his flame breath actually comes out, or you will trigger the ghost. Target time for this fight is 45 seconds, but it can go as low as a 44 in run conditions with perfect execution.
A typical King Boom Boo fight, hitting the hourglass as early as possible and getting 4 hits in one cycle. The angle to hold while getting the hits is roughly forward and left.