Hudson's adventure Island/Game Mechanics

Hudson's_adventure_island

Items

- Adds 128 to the small timer (corresponding to 80 on the end-of-level countdown)

- Adds 128 to the small timer (corresponding to 80 on the end-of-level countdown)

- Adds 256 to the small timer (corresponding to 160 on the end-of-level countdown)

- Adds 256 to the small timer (corresponding to 160 on the end-of-level countdown)

- Adds 384 to the small timer (corresponding to 240 on the end-of-level countdown)

- Adds a second timer countdown at the end of the stage. It also adds 135 frames of downtime between the two countdowns. This item should always be avoided at all cost.

- Visible eggs contain a skateboard, milk, stone axe, flower, fairy or egg plant. The content can always be predicted, but depends on whether you have a weapon and/or the skateboard or if you kick or shoot open the egg. The content of the hidden eggs either contain a key or follows an item cycle. The detailed knowledge of the item cycle is only of interest for a score attack. The only thing to remember is that it will contain the fireballs if you have the stone axe. If you don't have the stone axe, don't open any hidden eggs (as it will then skip the fireballs in the item cycle).

- Restores the big timer to 12 and the small to 255 (corresponding to 2060 on the end-of-level countdown)

- The first weapon

- Increases movement speed and allows you to take one hit

- Invincibility

- The timer ticks down with 5 times the normal speed. The egg plant leaves the screen when the timer is just below two on the big timer (see timing section below). The fast tick-down speed continues until the egg plant leaves the screen. The fruit route is therefore very important when collecting the egg plant, to make sure it leaves the screen at the right time.

- The second weapon. Found in a hidden egg if you have already collected the stone axe. The fireballs fly in a different arc than the stone axe and can also destroy stones and boulders. The weapons are equally strong.

- Found in hidden eggs. Collect the key and one of the coming platforms/clouds will take you to a bonus stage

There are more items, but they have no impact on a speedrun.

Level overview

Forest: 1-1, 4-1
Islands1: 1-2, 3-3, 6-1, 8-2
Cave1: 1-3, 6-2
Dark forest: 1-4, 2-4, 3-4, 4-4, 5-4, 6-4, 7-4, 8-4
Islands2: 2-1, 5-1, 7-2
Cave2: 2-2
Cave3: 2-3, 5-2, 7-3
Cave with moving platforms: 3-1, 5-3, 8-3
Rolling hills: 3-2
Mountain: 4-2, 6-3, 8-1
Ice cave: 4-3, 7-1

Movement speed

The character's movement speed is shown in RAM-address 05A4. The unit is "8 sub-pixels/frame".

Acceleration
3 - On the ground (no ice physics) or while dropping down from a platform (not a jump)
1 - Ice physics or while jumping
Note: deceleration follows the same rules (but with a negative sign)

Default speeds
Walking - 49
Running - 73-75
Tripping - 50
Skateboard braking - 32
Skateboard - 48
Skateboard + Right - 73
Skateboard + Right + B - 80-82

The game will every frame try to adjust towards the default speed. For example, if you start walking from a standstill, you'll reach speed 51 on frame 17. On frame 18, the game will decrease your speed to 48. On frame 19, the speed will be back at 51 etc. When the default speed is a range, any of the speeds is acceptable.

Observations

• The only way to consistently reach a speed of 82 when on skateboard is by following these steps:
  

1. Jump
2. Release B mid-air. Regardless of your initial speed, you'll revert to 73.
3. Re-press B after landing. After three frames, you'll be moving with a speed of 82
If done consistently throughout the a run, you'll save very roughly 15 seconds over not using this speed trick.

• If you're about to pick up a skateboard, make sure your movement speed is 73. This will ensure that the skateboard speed will be 82 (73 + 3*3). Getting 73 when on foot is fortunately easy. Just jump and shoot mid-air. Your running speed will then always be 73 (assuming you didn't shoot right before landing).
• A special case is when landing on skateboard (as opposed to running into it). In this case, the first two frames of acceleration from the skateboard will be by 1, instead of the usual 3. This means that a running speed of 73, will only result in a skateboard speed of 81 (73 + 2*1 + 2*3).
• In the ice stages, there is no way of getting a higher speed than 80 on skateboard. If you enter an ice section (1-3 and 6-2) with 82 speed, you'll however keep it until the speed is dropped to 80 or below (for example by shooting), at which point the max speed for the rest of the ice section is 80. The same reasoning gives 73 as the max speed in the ice stages when on foot.
• When on foot, it's not possible to consistently regain 74 or 75 once you've slowed down to 73 (which is always the case when for example jump shooting). 75-49=26, which is not a multiple of 3 (same goes for 74).
• By shooting sufficiently close before landing when on foot, your landing speed can't be predicted in real-time. However, as long as it's between 49 and 73 when you hit the ground, you'll have a 2/3 chance of ending up with a higher movement speed than 73.
• As long as you only shoot while on the ground (or while dropping from one platform to another), the top speed for your state isn't going to change. This is particularly important to remember when on foot since it's so much harder to regain 75. This obviously doesn't apply to the ice stages though.
• Setting up an 82 speed when on skateboard as described above costs ~1 frame (assuming the thrown weapon doesn't induce any lag, which is quite often the case). You'll roughly earn 1 frame back (compared with a speed of 80) every half screen. So for it to pay off with at least 1 frame won, you should be able to go one full screen with 82.
• Tripping on a stone costs ~11 frames, but also reduces the big timer by 2 (corresponding to 32 frames of countdown at the end of the stage). And not to forget that the running speed will be 74 after landing (50+8*3). So in some cases it can be beneficial to trip on stones.
• As a rule of thumb, doing a default jump (without holding down B or the d-pad) costs ~8 frames.
• When you hit the goal line, the speed is reduced until the base speed is reached. The acceleration follows the same physics as described above. That means if you jump right before the goal sign, your speed will be reduced by 1 every frame iso 3. However, this has no impact on the time it takes to end the stage as it's not related to when Higgins leaves the screen.
• Some stages have Higgins moving on slopes. This has no impact on the horizontal movement. (i.e. there is no benefit of trying to jump the slopes to try to avoid vertical movement)

x-position

The following RAM-addresses determine Higgins' position:
003A - The x-position of the screen (big). Starts at 1 and reaches 32 at the end of the stage (each stage is equally long). 8, 16 and 24 determine the checkpoints.
0006 - The x-position of the screen (small). When this address loops, one is added to the big x-position.
0584 - Higgins' x-position (relative to the screen). While the screen is scrolling, the value stays at 96. At the end of the stage, the goal is reached when the value reaches 128.
0574 - Higgins' sub-x-position. When this address loops, one is added to either 0006 (if the screen is scrolling) or 0584 (when the screen is not scrolling).

The boss stages are special cases as they are longer than the other stages. The boss triggers when the screen position reaches 32, 128.
By multiplying the value of 05A4 (the movement speed) with 8 and adding it to the sub-x-position, you can calculate the new x-position after a frame of movement.

Timer

RAM-address 0876 contains the big timer and 0877 the small timer. The small timer ticks down by one every frame (5 when cursed by the egg plant). When the small timer loops, the big timer ticks down by 1. Every stage starts with the big timer on 10 and the small timer on 255. However, the max of the big timer is 12 (it can actually go even higher, but that's by collecting items that aren't relevant for a speedrun).
Every 32 ticks on the small timer are worth 20 on the end-of-level counter. 20 on the end-of-level counter cost in total 2 frames of countdown.
A relevant case to mention is when the end-of-level counter is 0. This happens when you end the level with the timer at 31 or less. In short, this doesn't skip anything in the time it takes counting down at the end of the level. It's just two frames faster than ending a level with 20 on the end-of-level counter.

Speed tricks and other

Bosses

The first boss takes 8 hits. The bosses after take two more hits each time (so 24 for the last boss). The hits are stored in memory address 0672. Each boss shoots fireballs in the same spots. Since the boss is sped up for every area, the timing between fireballs changes however.
The timer for ending the level starts when the boss flies off screen (7 first bosses). The further the screen is scrolled to the right, the longer it will have to fly off before leaving the screen. The difference can be almost half a second.
There are essentially two options for fighting the bosses. With the right rhythm and finger speed, it's possible to get in 4 hits on the boss on each jump. Because of the limitation of only two weapons on the screen at a time, this is only possible at almost point blank range. This is the fastest, but also riskiest option. The second option is to attack from a distance. This only allows for a maximum of 3 hits per jump. In this case, It saves time to be as far as possible from the boss in order to not scroll the screen more than necessary.
The last boss always drops down from the rightmost position of the platform. You therefore need to adjust how far to scroll the screen to avoid it walking too much after taking the last hit.

Section skips with bonus levels

In 2-3 and 7-3, it's possible to skip the last section of the level. See the routing section for videos. The explanation is that if you hop on to the bonus platform while moving with the default skateboard speed (49), you'll barely trigger the checkpoint for the fourth section of the level before going into the bonus. Since the bonus stages always returns you to the section following the one you were in, this means you'll re-appear right before the goal. The setup is so particular and no other bonus platforms are placed in similar locations, so this trick only works in these two stages (and unfortunately there is no bonus in 5-2).
This trick was presumably found by the Japanese speedrunner 'Takenoko' (たけのこ).

Snake poison

Snakes spit poison if you during the level have thrown an axe against an object that bounces it off (stone, rock or egg). Combined with the fairy, it's possible to get a big score boost with this trick, but it doesn't have any use for a serious speedrun.