GD: Gradius II (AC) Rank System

[clymax]

A. Intro and Motivation

Spoiler

• So Gradius II (AC) is my current project in terms of modding in fanmade achievements. After some initial setbacks, I made some breakthroughs today in figuring out the rank system via reverse engineering.

• I decided to make this post because nothing appears to be documented for Gradius II as far as rank determination is concerned. This is even though such has been documented for Gradius I and III, here and here.

• These are my preliminary findings. As such, they may be incomplete. If you find something not mentioned, and you'd like to share it, please feel free to reply here or contact me via PM.

B. Rank System

Spoiler

1. Overview

The rank of this game appears to be determined by a simple addition of various components.

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Game Difficulty + Loop/Stage + Powerups + Special = Rank

• The gameplay difference between rank levels increases as you reach the higher ranges: 21->22 is a larger deal than 5->6, for instance.
• Deaths per se do not appear to have an effect on rank.

2. Game Difficulty

This is set on the DIP switches.

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1. Easy:      0
2. Normal:    2
3. Hard:      4
4. Very Hard: 6

3. Loop/Stage

This component is determined as follows.

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6*(Loop # - 1) + ((Cumulative Stage # Across All Loops) - 1) = Loop/Stage rank component

The following table shows sample values for this component based on loop and stage.

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Stage__________________Loop 1________Loop 2________Loop 3
1 Artificial Sun            0            14            27
2 Alien                     1            15            27
3 Crystal                   2            16            27
4 Volcano                   3            17            27
5 Revenge of Moai           4            18            27
6 High Speed Maze           5            19            27
7 Boss Rush                 6            20            27
8 Gofer Ship Interior       7            21            27

4. Powerups

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1. Speedup: +0 (no effect)
2. Missile: +1
3. Double:  +2 (TBC pending testing of the different types)
4. Laser:   +2 (same comment as above)
5. Option:  +1 for each
6. Shield:  +4 (includes Force Field)

5. Special

There are two special conditions for rank. Rank is sampled and updated at all times.

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1. Rank Limiter A - Rank is limited to 16 on the first loop.
2. Rank Limiter B - Rank is limited to 27 on subsequent loops.

6. What Rank Affects

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1. Enemy speed
2. Enemy bullet firing aggression
3. Boss behavior

Enemy bullet speed does not appear to be affected.

7. Sample Calculations

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Normal, Loop 1, Stage 1, Missile
2 + 0 + 0 + 1 = 3

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Very Hard, Loop 1, Stage 2, Missile, Option
6 + 0 + 1 + 1 + 1 = 9

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Easy, Loop 2, Stage 5, Force Field
0 + 6 + 12 + 4 = 22

C. Acknowledgements

Spoiler

• Special thanks to Speedway of the Retro Achievements community for helping me get some useful hints from the knowledge of the Japanese STG community, when my initial efforts were getting me seemingly nowhere.

• As one might suspect, this post is inspired by Seahawk's post here. Not only that, but the structure of this post was humbly but shamelessly taken from Seakhawk's post. As such, credit for the structure goes to Seahawk.

• Youtuber Toarcade for previously having posted some hints on when rank is suspected to become maxed.