EDIT: So during my 100% run, I noticed that getting what I thought was the minimum score didn't actually give me the pictures for some stages (Danger! Clams!, Bubble Burst, Bubble Rings, etc.) and I am extremely confused as to why. It appears that I'll have to do more work on this guide, but I unfortunately have no idea how the gallery pictures work. One theory I have is that the picture isn't given off the player's score, but the time spent in the stage. Or, perhaps the score required for it is simply different every time. Either way, this category's a doozy. Now, keep in mind that the following guide hasn't been edited yet. Some things may not work.
Upon completing a stage that isn't an Escape stage or Finding Nemo, you will unlock either the Score Attack, Time Attack, or Extra Play version of that stage. After getting over a certain score in these stages, you will be awarded with the gallery picture for that stage.
This guide will contain the lowest required scores for each stage, as well as some strategies that can be used to help achieve these scores as quickly as possible.
DISCLAIMER: Noted that all information in this guide has been obtained from the NTSC copy of the game. It's currently unknown if certain score requirements have been changed in other regional versions.
You can use this password to access all stages with no gallery pictures unlocked: RK3V?S9Q7W.
The Route
In Any%, the stages are played in an order that spends the least amount of time in menus. For 100%, the same stage order will be followed. The only major difference is that the Score Attack/Time Attack/Extra Play version of the stage (which I will be from now on referring to as SA/TA/EP), is played immediately after unlocking it.
The Stages
Individual stage score requirements and notes are covered here:
Escape Stages - Not covering each individual escape stage (at least for now), as they're all the same idea with different level layouts. To get the gallery picture, you have to find 16 squares which form a portrait of Nemo on the top-right corner and are scattered throughout the level. They're generally not too hard to find, but doing them fast requires memorizing their locations and the level layouts.
Shark Attack! (SA) - Minimum score required is 3 000. The bigger chains you get, the faster you'll approach the score. End the stage by losing all your health.
Minefield (SA) - Minimum score required is 5 000. Don't focus too hard on making chains. It takes quite a while to get to 5000, so it's more important to play it safe and avoid getting hit until the end.
Sea Urchin Peril! (SA) - Minimum score required is 3 000. Fastest way to get this score is to stay at the right edge of the screen. You can tank two hits, as you have to lose all your hearts to end the stage anyway. Once you're down to your last heart, play it safe until you reach 3 000 and immediately collide into the urchin closest to you.
Sounds of the EAC (EP) - Successfully complete any song. The shortest song is the fourth one: Green Road. This one is a little difficult to clear successfully, so you could opt to play the second song, Title, which is only 4 seconds slower.
Guide Dory (EP) - Enter Stage 10 and fail the stage as soon as possible. Very easy. You don't have to even beat the level.
Danger! Clams! (SA) - Basically a matching game. Minimum score required is 2 800. Apparently, the pairs are randomized.
A Helping Fin (TA) - Ok. I know it says Time Attack, but this is more of "how long can you survive" kind of thing. Survive for 3:00.00.
EAC (TA) - Survive for 1:30.00.
Starfish Rock (SA) - Minimum score required is 5 000. Nothing you can do to speed up the process. Just don't lose.
The Harbor (SA) - Minimum score required is 3 000. Balance between avoiding seagulls and grabbing as many feathers as possible.
Jellyfish Dodge (SA) - Clear 15 rooms and lose. The first room is always the same and the key is in the top-left corner. The exit you need to take after picking up the key is always random.
Danger! Eels! (SA) - Minimum score required is 5 000. Be careful. This is kinda tough.
Bubble Burst (SA) - Minimum score required is 6 000.
Bubble Rings! (SA) - Minimum score required is 3 000. Make sure to chain combos but not misinput until the end!
Bubble Puzzle (SA) - Minimum score required is 3 000. Try to avoid using green bubbles unless absolutely necessary.
Crab Challenge (SA) - Minimum score required is 10 000. This one is complete bullshit. I can't give you any advice, only moral support. Sorry.
Lobster Rescue (SA) - Minimum score required is 2 000. Smaller lobsters are worth more points, so if two spawn, you save the time it takes to do an extra claw grab.
Coral Caves (SA) - Minimum score required is 3 000. The stage layout and coin placements are entirely random.
Pearl Smash (SA) - It's a best-of-three match. Winning a match earns you a point, losing ends the entire stage. Get 5 points, then let the opponent win.
Bubble Battle (SA) - Defeat 5 anglerfish and lose. Be careful though, the AI can either absolutely snipe and destroy you, or wander aimlessly and miss every shot. There's no in between.
Crush the Blocks! (EP) - Enter and complete Stage 15. Good luck.
