Celeste

The cassette to unlock these levels can be found fairly late in Chapter 3 after Mr. Oshiro blocks your path and tells you that you're almost there. After that, you can access them any time from the map. I recorded a quick walkthrough of both the cassette and the B-Side:


Timestamps are in the description, and I've also included a couple tips to make some of the moves make a bit more sense

Since this will be your first B-Side, I'll do some explaining
The B-Sides are unlocked after finding the cassette in the A-Side, or normal version, of their given level. So, for the B-Side of Chapter 3, starting from Section 3, you'll travel up through the shaft overhead and head left through several rooms until Mr. Oshiro stops you and has a chat. Head down after that and through the next room. Travel clear across this room and enter the room on the left after the key to find the cassette room on the other side. After collecting the cassette and finishing the level, you'll get your rundown of strawberries collected and total deaths, plus the unlock for the B-Side.

B-Sides are more difficult version of the given chapter, with the same theme and mechanics of the level, just turned up to 11. The sections are roughly the same length as their A-Side counterparts as well. Every B-Side ends with an alternating pink and blue platforming section with their Crystal Heart at the very end. Plus, they have a bangin' alternate version of the level's theme song. That should be everything, so let's get into it. I'll break each section down into their own parts so they're easily identifiable.

Section One

• Simply dash across the large gap.

• Use the jump pad and dash to the second stone wall. Climb up and jump to the left side of the next wall, then to the last wall and jump over the spike to its right side. Jump to the green gem and dash up-right to the second stone wall. Jump over and grab onto the left side of the next wall, then jump over to the right side and jump to the ledge ahead and exit right.

• This room is very simple. You just need to jump from one side of each block to the other to cross the room while avoiding the circling orbs. Some of the blocks have the worm things on top of them, making it impossible to backtrack. Otherwise, the only block that may cause issues is the last one, which falls after a short time of landing on it. Exit right into the next room.

• Jump to the wall as the orb slides down to give you the most time to move. Climb up and jump over the wall as the next orb is sliding down. Slide down and jump across the gap, dashing up to grab onto whichever wall you can reach. Grab the green gem and prepare to jump right and dash to the next wall when the orb there slides down. Climb the wall and jump over when the orb slides down. You need to slide about 70% of the way down the wall to jump into the small gap to exit right.

• Use the jump pad to launch you up, then dash over the wall and fall down the center to grab the green gem and grab onto whichever wall doesn't have an orb barreling towards you. Climb to the top and get on the right wall, then jump and dash over the wall ahead as the orbs are resting on their walls. Fall down the center and grab the green gem and either wall. Climb up the left wall past the orbs and jump and dash to the last vertical shaft, fall past the orbs and exit right to the next room.

• Use the jump pad and dash to the upper left wall to assess the situation. There are three blue gems in this room: one in the upper vertical shaft with two orbs climbing walls, one below the pacing orbs and jump pad near the bottom of the room, and one in the upper-right corner with an orb pacing up and down just before gem. Drop down and use the jump pad to refill your dash, then dash up to the blue gem in the shaft. Fall back down to the jump pad and go into the upper corner for that blue gem. Lastly, fall down to the jump pad for a refill, then grab onto one of the lower walls underneath the jump pad and wait for the orb to pace to the opposite side to jump to the gem and dash upwards to clear the incoming orb and land back on the jump pad. Head right and dash to the end to exit right.

Section Two

• Dash up and grab the wall, then jump onto the first moving platform when the circling orb crosses over the top of its path. This will set up the cycle ahead to be just right for us to keep moving. Ride the platform down until just after the vertical pacing orb starts to go down, then jump and dash up-right to clear it and land past the circling orb ahead. Do that again and wait on the last platform until you're below level with the gap ahead and the circling orb is at the bottom of its path to jump and dash through the gap. Dash up to the end from there and exit right.

• The walls here have a small amount of space at the top that is clear of the pacing orbs, so use that to your advantage to cross this room pretty much unscathed. Save your dash for the death column, then exit right.

• Jump as the pacing orb starts moving right for the optimal cycle. Jump and dash to the next platform, then jump and dash to the wall overhead and bounce off of it and the next wall to reach a green gem. Dash up-left and land on the right side of the platform to avoid the orb. Jump over it and dash up-left to the left wall as the orbs start moving, then climb up when those orbs start moving to reach another green gem, where you'll dash to the end and exit through the ceiling.

• Jump as the first orb hits the lower platform, then dash up to land on top of the block. Jump and delay your dash up so that you can wait for the orb to pass by before landing on top of the second block. Jump past the third orb and dash right to land on the third block. Jump and dash up-right to grab onto the right side of the wall ahead, then jump to the last block and jump and dash right to exit right.

• Jump and dash up when the first orb hits the bottom of its path, grabbing onto the wall and quickly jumping off to grab onto the right wall as the orbs move. Bounce back and forth between the walls to avoid the orbs as you climb towards the green gem, then dash up and wall bounce off the small walls to clear the long fall of orb walls, grabbing the gem on the way down. Dash into the small gap and exit right.

Section Three

• Use the jump pad to boost you over the single spike on top of the wall, then dash to the right wall and climb up, avoiding the moving orbs. Jump for the green gem and repeat that twice, the last time dashing for the wall at the end so that you can jump up to the small wall and exit right.

• Jump and dash to the first wall and jump through the gap when the orbs settle, grabbing onto the other side. Jump to the next wall and repeat twice, landing on the jump pad to reset your dash and stamina. Hold a hard right off the jump pad to clear the wall and dash up to grab onto it from below. Climb up and jump over the orbs ahead to grab onto the right side of the wall below. Repeat for the last wall and jump to the end to exit right.

• Just like two rooms ago, you'll need to climb and jump over walls while avoiding orbs, but with twice as many this time around. You can jump off the last wall attached to the ceiling to the end to skip the final floating wall with orbs. Exit right.

• You need to wait for the orbs to be in their upper position before you can walk off the edge and dash right to safety. Do the same thing here, but dash left as you fall to land safely. Lastly, jump and dash right to clear the orbs and exit right.

• As the first orb starts to move up, jump and dash up-right to pass the first orb and bounce off the jump pad. Dash up-right past the second orb and use the jump pad while holding right to approach the next orb. Dash right as you clear the orb walls overhead to pass the third orb and use the jump pad below. Dash right to pass the fourth orb, then delay your dash to pass the fifth orb or else you may be too quick and catch it in the head. Use the last jump pad and hold right, then dash into the green gem and dash up-right just before you would come in contact with the ground below to reach the next gem. Dash to the jump pad and fall between the two groups of orbs until the second group starts moving up, then dash up-right to the last jump pad. Hold right and dash right to pass the final orb and exit right.

Section Four

• Dash up through the ceiling to start the Mr. Oshiro section, where he tries to take you out much more often than in the normal level.

• Dash up-right to the first wall and bounce between the three walls to reach the top. Stall for Oshiro to zoom by and jump over the wall, grab the green gem, and dash right to the wall ahead. Climb the wall and stall for Oshiro again, then fall down to the bottom wall and jump off of it to reach the green gem. Dash up-right to grab onto the wall ahead. Jump over it and grab onto the opposite side, then jump for the middle wall. Jump over that one and grab onto the opposite side, then jump for the jump pad on the floor to reach the final wall. Jump over it and continue right.

• As you cross the screen, there will be some open areas above and below that are used to avoid Oshiro as he zooms by. There are four such areas, and you'll need to dash from the first to the second one to make it safely.

• Jump and dash through the small gap to use the bounce pad on the other side to boost you up and dash through the next small gap. Hold right to grab the first green gem, then dash up-right to get the second gem and hold right, then dash through the gap to exit right.

• Jump and dash for the first gem, then dash right until Oshiro zooms by, where you'll want to dash up or up-right to avoid him and still be able to grab a gem and continue dashing right all the way to the end.

• Wall bounce between the first two pillars and stop at the top for Oshiro to zoom by as you jump for the first blue gem. Land and grab onto the right wall ahead, then jump for the green gem and fall between the next two pillars to grab the blue gem below and dash up-right to grab onto the next wall. Climb up and jump to the next wall, then jump for the green gem and fall for the last blue gem, then dash right to grab onto the small wall and wait for the large block to clear the hole to enter and exit down.

• Just before the pink jump pad block goes dark, jump and dash through the small gap, then dash through the next gap to land on the jump pad and dash up to grab the first blue gem above. Fall down to the second blue gem and grab onto the wall. Climb up and stand on the edge of the platform, then jump out to the left and dash up to grab the third blue gem and clear the floating orb, landing on the right side of the platform. Wait for the blue block to be dark to jump and dash for the last blue gem, then use the jump pad below to refill your dash and boost you up high enough to dash up-right through the last gap. Dash into the heart and enjoy your achievement.

Timestamps: 52:32 & 56:44