Difference between revisions of "Mighty Bomb Jack (NES)/Game Mechanics"

Revision as of 12:32, 9 September 2013

Mighty Bomb Jack (NES)

Items

The following items are of interest in a speedrun:

• Mighty coins - Found in chests (always in the same location). Jack can hold up to 9 coins at a time. Picking up a tenth coin sends him to the torture chamber (very bad). When using mighty coins, Jack gains different abilities:

1. coin - Jack turns blue. He can now open locked chests by jumping on them. Jack turns back to normal after pressing A 20 times.
2. coin - Jack turns pink. Same effect as blue and he can now also open chests (both normal and locked) by running into them from the side. Jack turns blue after pressing A 10 times.
3. coin - Jack turns green. Same effect as pink, S-coins can be collected and all enemies turn into coins for a few seconds. Jack turns pink after pressing A 6 times.

If Jack uses a mighty coin while being blue/pink/green, it doesn't matter how many jumps he made previously. The jump count is always reset.

• S-coins - Found in chests (always in the same location). There are in total 10 (?) of these coins. In order to get the best ending, you need to collect 5 or more (there is no point in collecting more than 5 though).
• Crystal balls - There are two crystal balls in the game. Both are found in special chambers, where you need to break some of the blocks surrounding them. In order to get the best ending, you need to collect both of these.
• Sphinx - Some doors are hidden or locked. The only way to open these is to find the corresponding sphinx (sometimes there are more than one sphinx in a room and each one corresponds to one door).
• P-ball - All enemies turn into coins for a few seconds. The P-ball is spawned by collecting bombs during the stages and in the palace rooms. The required number of bombs seems to be different for different levels (to be confirmed). If this happens during the stage, the next chest will contain this item. If it happens in a palace room, it will spawn in (or near?) the center of the room and start moving around diagonally. The counter is reset every time you reach a new level.
• Bottles - Increases the timer. Should be avoided in a speedrun as it wastes time counting down after the end of each level.

Jump mechanics

Holding up while pressing the jump button creates a higher jump. For roughly the first half of the screen, it's very similar to a normal jump. The vertical speed of a normal jump then starts to decrease faster than when holding up. Holding down during a drop increases the acceleration initially. This should be used as often as possible in a speedrun. The max drop speed is however the same as dropping normally.

Enemy behavior and manipulation

There are only six (seven if you count the mummy) different types of enemies in the game. Enemies start out as mummies. The mummies walk back and forth on the platform they spawned on, but eventually drops. When they reach the floor, they transform into one of the six enemy types (these are not the official names, I hope they are understandable though):
0. Bat - Moves around diagonally without considering Jack's position.
1. Lobster - Fast moving enemy that homes in on Jack. (in most situations, this is the most dangerous enemy)
2. Jellyfish - Moves seemingly randomly, but every time Jack hits a wall or the ceiling, the jellyfish will fly to that spot at full speed.
3. Skull - Homes in on Jack horizontally, but cannot control its vertical movement.
4. Fireball - Homes in on Jack vertically, but cannot control its horizontal movement.
5. Bird - Slow moving enemy that homes in on Jack horizontally and vertically. It can't move diagonally.
The enemy type is determined three frames before the mummy starts transforming. The game then looks at the value of memory address 00FA and calculates the modulus of 6 of that value (= the remainder when dividing by six). The numbers in front of the different enemy types indicate these values. The value of 00FA is increased by one every time the jump button is pressed. This means it's very much possible to manipulate the enemy spawns in certain areas (and it's also crucial to take it into account in a speedrun).

Enemy spawning is only partially understood by me. Most (all?) of the time, spawning locations and initial enemy behavior (for example: start by going left or by going right) depend only on Jack's position. Certain sections of the screen yield different results. It's often fairly complicated however. While this might be difficult to exploit to its full extent, it can readily be used in some areas to get the desired result. The best is to keeping in mind the possibility of manipulating enemy spawns when exploring different route options and apply findings on a case-by-case basis.