Cotton 100%

This achievement (along with "Got the top score!", "You are getting there!" and "You can do even better!") is awarded for reaching the score in Challenge mode without dying. When I say dying I mean using a continue which sets you score to zero. Unlike all the other achievements in the game, this is not easy. If you aren't good in these kinds of games, you can still do it with a bit of practice. I would suggest to leave this achievement for last. By that time you will have a good enough knowledge about the game. While you can't use any rewind or cheat functions in this mode there are still ways to make this much easier.
Warning: Due to programming mistakes there are a few ways to accidentally enable Standard mode cheats and Rewind in Challenge mode, like dying and resetting the game from the main menu on a specific frame. While you can complete the "Challenge" mode this way (it can result in inverted colors but everything else works) the game won't unlock the achievement. Also if you enable the original SNES cheats the game will block all achievements until you delete your entire Xbox save.

Before you start the Challenge run, select the Config menu (in game). Set the difficulty to easy and the lives to 9. Choose the fourth set of magic. You will only need the fire breath Magic but the third magic bubble could come handy if you are down to your last lives. It blocks a hit. Don't despair if you die to dumb hits in your first runs, you will improve a lot with a bit of practice. You don't need to finish the game so you can "waste" magic on some bosses to make sure they don't kill you. The most important tactic is the same as for the Standard 500k score: avoid picking up anything during Tea Time. You don't have Rewind in this mode but you have the power of PAUSE ! At the beginning of TT, move at the bottom of the screen and pause the game as you see the bonuses coming. The rule of thumb is there is always a big gap somewhere but the gap doesn't stay there for long so always look for an escape. Move to safety the pause and asses the situation. This doesn't guarantee you can get the bonus but makes it very likely you will be able to nail it a few times which is more than enough for the 500k. For some reason TT on later levels is easier so don't despair if you keep messing it up.

For the generic enemies there is not much to say. Most will die extremely quickly on easy, you should rarely if ever die to them. There are a few dangerous ones you should watch out for:
- Hiding enemies: there are various enemies at the bottom of the levels you can only take out with a bomb. While these are harmless most of the time you should bomb them because they tend to jump out and block your way eventually.
- Laser "frog": Depending on your firepower level you can take these out in a second or they never die. Since they are extremely dangerous I would suggest flying above them if they don't die asap and giving up on the magic refill.
- Archer: the arrows can slip through your bullets with ease. You should either fly high and avoid them or watch the arrows and quickly duck in front of them. Don't try to just barely hit them with the bottom of your bullets because they will hit you. Either commit to a frontal assault or fly behind them.
Most of time you are the safest at the left side of the screen, but some levels (like the underwater one) require you to stay somewhere at the middle at certain portions. Level geometry is usually safe (even the lava river at the chicken boss!) except some laser grids and lava balls.

Boss guide
Hold on your magic for the bosses. Most are easy and die quickly but if you feel you can't take them down for sure then spend a fire breath on them. It should either straight up kill them or kill them after a bit of normal shooting. Magic is not easy to come by, especially if you struggle with the frogs so I will describe how to take the bosses down with no damage. In general you should stay on the left side of the screen, the furthest possible from the bosses. If you are using magic always do it by "hit confirming" the attack. Shoot normally and if the enemy is flashing then send out the fire breath. This is especially important if you want to kill a boss as soon as possible because it might still be invincible while you are able to act already. A wasted magic just leads to frustration and might lead to taking unnecessary risks to replenish it!
Clown head (1-1): First boss in the game so it is extremely easy. Just stay on the left side until it comes close. Then circle above and around him. When it will come back then go back to the left side under him. Should die in just one cycle.
Pumpkin pilot (1-2): You can stay on the left side and shoot it. No need to avoid it. It will stop in front of you and fly back. I would suggest shooting the bombs on your side of the screen to avoid one of them randomly hitting you when it does the hammer move.
Bee flower (2-1): If you didn't die so far your fairy companions should cover the bees it sends out. You might need to move a bit upwards sometimes.
Batting snowman (2-2): Again, if you have your fairies they should cover the snowballs. Just stand in the line of the ball. If you don't reposition quickly enough the snowman will live long enough to jump towards you. duck under him and stay on the right side of the screen until it comes back.
One eyed mushroom (3-1): I don't like this one so I tend to spend a fire breath to kill him right away. But you can kill it normally if you stand around the middle portion of the left window before it launches the spike balls. Nothing should hit you in the first cycle and it should die by the second.
Mechanical worm (3-2): This one is either easy or hard, depending on RNG. If it doesn't come out the left hole you can shoot freely. If it comes out you should stay around the middle of the screen. When it does the bites in the second phase you should circle around it to the other side. If you aren't confident you can fire breath it away.
Ent and Chipmunk (4-1): I hate this one, a lot of ways to die. You can delete it if you fly to its mouth and release two fire breaths. If you want to beat it legit you should stay near the bottom and the left side the screen while moving a bit up or down - watching for the exploding fishes. Move between the branches as needed. The key is to be low enough to end up under the large horizontal branch it sends out from time to time. If you end up above, the Chipmunk will destroy you while you can't deal damage. If you end up under the branch you can shoot the mouth freely. Still, it takes several long cycles even on easy this way so I would suggest the fire breath. If there is one boss you should use magic on it is this one.
Doll and head (4-2): Probably the most random boss in the game but I would suggest not using fire breath no matter what. Due to the randomness the doll or the head might be invincible for a random period of time which means wasted magic. If you stay on the left side you can deal a lot of damage before they come close. There is really no other suggestion other than to try to slip behind them when they come close. The head is slow and predictable but the doll tend to do large jumps. The safest place is the top left side then. I never really died to them but some battles got very intense. One of them usually dies very quickly and the other one is much easier to deal with.
Rock elemental (5-1): If you start shooting right away and have some fairy backup it should die by the time it comes close.
Lava chicken (5-2): You are relatively safe in the top left corner when it comes close but you can breath it away if it feels too hot (heh). Really both this one and the rock boss is very easy IF you don't lose all your fairy companions (which might be a tall order on this level).
Hermit crab (6-1): Extremely easy. Just stay at the bottom left side and shoot. The small enemies it sends out will lose their invincibility bubble just before they reach you and you can kill them without moving. The only hard part is the battle takes way too long because there is only a brief period of non invincibility for the boss.
Water snake (6-2): During the first stage just stay on the left side and shot the green bubbles along with the boss. When it comes close just duck under and wait until it goes away. During the second stage try to pop as many blue bubbles as you can then stay at the top or bottom left part of the left side and move to the other side as soon as it lashes out.
Mirror Cotton (7-1): First I thought I will have to avoid stage hazards while chasing her but nope. Nothing special. She just shoots fireballs and throws bombs if you are under / near her. Save your magic.
Giant warrior fairy (7-2): If you are this far and still require points for the 500k then I'll have bad news for you. You either have 5 fire breaths in your pocket or you are toast. If you have then good news! Hit confirm and breath away! You can expect 20-30k+ from the encounter if I remember correctly. If not then you'll need to dash through or duck behind her energy pillar attacks which is hard even with rewind. Her pillars tend to dissipate before she powers up. Her dash attack is relatively easy to avoid but do it diagonally or you will be hit by the explosion afterwards. There is also a shield throw I rarely saw. Trust me you don't want to rely on this battle for score!