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Rock 4
At the beginning of the level, toss fire and grab bomb. We toss fire here because it's really slow to do so underwater at the end of 2-3. After getting past a few enemies, let the Nruff pass you and then jump on the edge of the purple platform. In the elevator section, float up and damage yourself on these two shotzos. The gap between the shotzos is enough such that usually you won't lose your powerup, but it's still possible. To ensure that the powerup isn't lost, wait for Kirby's "panic" animation to show up before doing the second damage boost. Of course, if you're low on health, do fewer hits.
The strat shown on the left is what some of us refer to as "TAS Blocks". When you get the jumps correctly, it's faster to fall in and grab Shard 1 before combining for lightbulb. I like to do a short hop after the ledge grab to fall into the hole faster, but there's a small risk of jumping too high and faceplanting. In 100%, it's always better to go to the left side because the backup (right), where you grab the powerup first, is no faster if you start on the right side. When combining for lightbulb, keep in mind that the Spark-i can shoot at you, breaking your powerup if thrown. I also like to jump before inhaling because the powerup bounces up when it just gets combined.
Using the lightbulb, light up the panels in the background and press the corresponding switches for Shard 2. The switches don't have to be pressed in order, and you can jump after pressing a switch to cancel the animation. Since walking speed with lightbulb is really slow, you should immediately stop using it once you've memorized the images. After exiting by jumping up the ladder, float up and skip the whole room. When on the elevator, take out the powerup in preparation for the miniboss.
During the miniboss fight, we want to defeat it as quickly as possible while getting double spark, a powerup useful for Pix. The lightbulb can be used to deal two damage, while we swallow a mini Spark-i to do the remaining two hits. My strat is shown on the left, while a safer variant is in the middle. A crazy idea to save a few seconds is to just fight the miniboss with lightbulb (right), risking huge potential time losses in the Pix fight. In all cases, jumping up the ladder is faster than floating up.
In the last room, it's fastest to jump up the poles. The spawn pattern on the right is tougher than that of the left, so unless you want to save the amount of time it takes for Kirby to turn around, it's better to go to the left.
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