Since there's not a guide for this, I decided to write one. It's not a very hard fight, and if you've played Metroidvania games or pinball games, it's not particularly difficult to get to the location, either. However, I was having a hard time thinking of how to describe the path to get there. Then I found THIS:https://gamefaqs.gamespot.com/pc/206092-yokus-island-express...
It's not perfect, but this is a pretty good guide from https://gamefaqs.gamespot.com/community/TestaALT
(Andrew Testa) at gamefaqs. Used in combination with the in-game map, it should get you all the information you need for this achievement.
Again, this is someone else's guide, and I take no credit for writing it. I just thought it would be good to include it here, since there's not a guide on TA, yet.
Getting to Screetch
Screetch is the first boss that you'll beat if you're following the walkthrough, and he is the goal of the second main objective of the game (the first being help Spina). From the Skull Hideout, go right and you will reach land with what looks like horns are going up. Simply roll off the right side of the screen and you will drop back down to the water pressure table you were at when you helped Spina.
Here, follow the tunnel down and you will drop into the fast travel been system, which will take you to The Underdark. Here, swim under the water to the southeast and go into the area in the middle under the water. Use the yellow flipper to hit the pinball into the the wooden swivel into the center. Do this a few times to spawn a few Unlock Coconuts. Get them, them go north. Press the button on the small platform, then swim out to the left. The current will take you to a pond area with a fallen stone statue in the background. Swim down and grab the two Unlock Coconuts in the water, then head left.
Continue left into the circular stone entryway and you will reach a new table. This one has three crystals blocking a northwest lane. Aim the yellow flipper so that it breaks each of the crystals and collect the Unlock Coconuts that spawn. When you've collected all of the Unlock Coconuts, the square area above you unlocks. Use the blue flipper to hit up to it, then collect the three Unlock Coconuts here. This will unlock the left lane, so use the yellow flippers to bounce through it. Continue left to reach yet another table.
For this table, bounce into the slug bubble a few times and suck up a slug. Then, destroy all of the dark rocks in the middle of the screen. After destroying two of them, aim for the middle to get the Unlock Coconut in the crevice. With that one, you just need to get the Unlock Coconut on the top lane. To get that one, swivel through the lane below it enough and the barrier will unlock. Then, go through the top lane to get the last Unlock Coconut. From here, you must hit into the top lane on the left side, then hold down the blue flipper so that you go through the new lane.
Back on land, go left and enter the circular stone entryway to reach another table. For this one, collect all of the Unlock Coconuts on the bottom of the screen by repeatedly going through the wooden swivel on the right. Afterward, bounce up to the top of the table and repeat this process with the yellow flipper and the wooden swivel on the left. When you've collected all of the Unlock Coconuts, the barrier on the left disappears, and you can enter a new lane. To get to this lane, hit normally with the yellow top flipper until you get in the lane on the left, then hold down the yellow flipper button so that the pinball goes into the chamber to the left. From here, press the yellow flipper button again so that the pinball bounces through the lane.
You reach a room with gold in it. Use the Noisemaker to turn the gold into fruit, and collect the fruit. Head out the right side, and continue right to reach the Ancient Birthing Grounds. Here, talk to the NPC in the dark clothes, Sal, then talk to the NPC in the red clothes. Head left, then talk to Ebon again and use the multi-color bumper to go up a level. Go left and eventually you will roll off and end up in The Crystal Deep.
Here, you meet Ebon again. Use the bumper to ascend a level, then roll to the left. Unlock the bumper at the end, then bounce up and go left. At the far left side of the level, you will find square buttons on the ground. Roll over all of them, talk to the NPC, then collect the Unlock Coconut. This will reveal a giant face imprint with a silver railway around it. Get on the bottom of it, and use the bumper to bounce up into it, then exit it via the northeast bumper.
You will go out to an area with a blue flipper and several crystals above it in a lane. Keep flipping the pinball until the crystals until they are all broken, then collect the Unlock Coconuts, and finally, drop down to the yellow bumper below. Here, again, break all of the crystals, and then go back up to the blue flipper and bounce in the silver railway. This will lead to a crystal with a monk inside.
Afterward, go left, use the multi-color bumper to go down, then head back to the circular railway. Use the southwest exit this time, then go right through the stone entryway to reach another table. For this table, hit the slug bubble, suck up the slugs, and break through each of the dark rocks. After that, you want to get the pinball in the far left gray hole. When you do this, it will bounce between holes and stop on the bottom lane, breaking all of the crystals on the bottom lane. From there, you want to collect all of the Unlock Coconuts that appears from breaking the crystals. After that, use the far left gray hole again to bounce out back to the red NPC. Talk to him -- he's Jet -- then use the multi-color bumper to bounce up. Head left, and use the circular railway and exit via the southwest. Use the bumper going down, and you will reach another table.
For this table, you must destroy all four of the purple crystals inside their respective spiraling lanes. To do this, aim wide or narrow with the respective flipper. When you break a purple crystal, it spawns an Unlock Coconut. Collect all of them, then go through the silver railway directly in the center. Afterward, head right and go inside the circular stone entryway. Head to the left, past the three NPCs, and interact with the door. Continue left and the ground eventually breaks beneath you.
You end up in water. Swim to the left, then use the blue bumper and bounce off the mushrooms. Head left and bounce up to Screetch's Lair. He is the first boss of the game (depending on where you go first).
Boss Battle: Screetch
For this battle, the red NPCs you found help you. To begin, destroy all of the yellow crystals on the screen. Afterward, your goal is to hit the top-right ceiling of the table. This will cause the boulder go drop on the slugs, which will break the dark rock and allow the red NPCs to enter the table.
The NPCs become red balls, and they can return to form on the table if they hit the swords. It does not really matter whether they hit the swords or not because they will turn into balls again after a little bit. Your goal is to break all of the crystals and then to enter the hole in the center of the screen. This will cause Screetch to open his arms, revealing his eye.
Now, you must hit Screetch's eye with all of the pinballs. There is no time limit here, so just keep hitting it with the pinballs until 1/3 of his health is gone. From there, you must repeat this process two more times -- break the crystals, enter the hole in the center, and hit the eye -- until Screetch dies. There is no way that you can die in this fight, and nothing is timed. This is a fairly easy boss fight.
After the fight, enter into the lane in the top-center and talk to Sal again to complete the quest.