Hudson's adventure Island/Game Mechanics

Items

- 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 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.

- Collect the key and one of the coming platforms/clouds will take you to a bonus stage

- Visible eggs contain a skateboard, milk, stone axe, milk, 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 follows a cycle. The detailed knowledge 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 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.

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 unspecified (sub-pixels?).

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 on stone - 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

• By releasing B in the air when on skateboard, you'll always land with a speed of 73. If you then press B, you're guaranteed to reach the game's max speed of 82. If done consistently throughout the a run, you'll save very roughly 15 seconds over not using this speed trick.
• 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, 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.
• 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 far from always 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 16 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.

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. On each stage, you start with the big timer on 10 and the small timer on 255.
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.

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). 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 here (and unfortunately there is no bonus in 5-2).

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.