When items drop in Maze of Galious

Door Bas Wijnen

Resident (34)

afbeelding van Bas Wijnen

19-11-2022, 10:25

In a comment to my video on the generated MoG map (https://youtu.be/QatXloCTusE), NLeseul asked about item drops.

I hadn't looked at those yet, but I have now. I've documented them in the github repository where all the code for the project is. Here's a copy of the top of that file (the file also includes some tables for convenience).

Drop type is defined by enemy type. Each type is linked to two properties:
Table starting at 547c@4: when-type; defines when to drop something. Range 0-4.
Table starting at 64e6@4: damage: defines vitality points lost when hit by enemy

The what-type (what is dropped when it is killed) is computed from the damage:
damage 0-2: what-type = 0
damage 3-5: what-type = 1
damage 6-8: what-type = 2
damage >=9: what-type = 3

Drops happen for (at most) 2 enemies of each type per screen, so a total of 4 dropped items. If there are more than two enemy types on screen (not sure if that ever happens), only the first two types that are killed will drop items. Of those types, specific enemies will drop:

when-type 0: Enemies 1 and 3. (So the first enemy killed drops an item, the second doesn't, the third does, and none after that do.)
when-type 1: Enemies 2 and 5
when-type 2: Enemies 4 and 6
when-type 3: Only the last enemy of this type on screen
when-type 4: Those enemies never drop an item

what-type 0: 1 coin (8/16), 10 arrows (2/16), 1 key (1/16), nothing (5/16)
what-type 1: 4 coins (9/16), 20 arrows (2/16), 1 key (1/16), nothing (4/16)
what-type 2: 7 coins (10/16), 30 arrows (3/16), 2 keys (2/16), nothing (1/16)
what-type 3: 10 coins (10/16), 40 arrows (3/16), 2 keys (2/16), nothing (1/16)

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Van Manuel

Ascended (19227)

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19-11-2022, 12:02

That explains the massive drops you get when slaying the hairball for instance?

Van Bas Wijnen

Resident (34)

afbeelding van Bas Wijnen

19-11-2022, 17:00

No, the hairball is special. I also found which enemies produce these "fountains" of items, but didn't look into them further. However, it's worth noting that the hairball and the "bird dragon" are both what-type 2, while other "fountain" enemies (Ill, Cyclop's Ghost and Maner) are what-type 3. I'm not sure what those others are referring to, I just took the names from the trainer.tcl file in openmsx. Anyway, it's possible that those others produce fountains of more valuable items than the hairball and the bird dragon.

I was only talking about enemies that drop a single item here. What it means to drop 2 keys is that there is a single key item that shows up when the thing is killed, but when you pick it up, you inventory receives 2 keys. And similarly for coins and arrows. The numbers in parenthesis for the what-types are the probabilities with which the drop will be that thing. As you can see, there almost a 1/3 chance (5/16 to be exact) that a what-type 0 enemy will drop nothing. And there is 1/2 chance that it will drop 1 coin. On the other hand, a what-type 1 enemy has a slightly higher chance to drop coins, and when it does, it will always drop 4 coins. A what-type 3 enemy like the bouncing ball is very unlikely to drop nothing (for the ones that drop, according to when-type): only 1/16.

On one extreme end there are the most worthless enemies: the butterfly and mini-bat, for which you need to defeat all of them on the screen, at which point you get a single what-type 0 item (so you could as well have killed a single worm for the same result).

Another one is the vertical blob, the ones that fly into the screen from below. Those are when-type 2, so you need to kill 4 of them before an item drops, and that item is also what-type 0.

The other extreme are the most valuable, which are what-type 3. There aren't many of those though and some can't even be killed enough times to drop anything (for example, the lizard with the tongue in world 9 needs to be killed 4 times before it drops something, but there's always only one in the screen, and the counter resets when entering a new screen). There is the water strider, which needs to be killed twice, but in many cases it will be hard to pick up the loot.

Slightly less valuable (what-type 2) gives more options, even of when-type 0 (so you only need to kill 1 of them to make it drop loot): The most interesting one, I think, is the Gorilla.

Early game, none of those can be found though. So for maximum loot early game, I think the best you can do is the bouncing balls at what-type 2 and when-type 1 (so you need to kill 2 of them for a drop).