The game

A horizontal scrolling shooter: the Metalion ship against Dr. Venom, planet by planet. Everything on this page is read in the code and the pictures are drawn from the ROM.

The title

The title is built by p01:615B and its texts by p01:61C1. On a Japanese MSX (BIOS byte 0x002B) the logo reads GRADIUS, and the story and ending texts come out in Japanese.

The stages

The map has twelve stages (0xE201). The game starts at stage 1 with 3 lives (p00:5AD8). The next one is decided by p01:7C59: it goes up from 1 to 7, and then down from 6 to 0 with 0xE20A odd, which in many places brings more enemies and more shots. Stage 0 is the final fortress, 8 is the interior of each boss and 9, 10 and 11 are secret. Each stage has a checkpoint (p01:694A) from which play resumes after losing a life.

The maps are built from their metablocks (p13:7900, p00:4889):

Stage 0 Stage 1 Stage 2 Stage 3 Stage 4 Stage 5 Stage 6 Stage 7 Stage 8, the interior Stage 9 Stage 10 Stage 11

What closes each stage is in its script (p01:7A34):

Stage	When the scroll ends
1	boss 1
2 and 3	boss 4
4	600 more frames, boss 5 and then boss 2
5	a 600-frame corridor of hatches and then boss 2
6	two pieces that throw rocks, no boss
7	boss 3
0	a core of 100 hits

The enemies

There are 65 enemy types, each with its 7-byte record (p00:4F4C). Each stage brings those of its list, its generators, its wave and those dropped by the objects and bosses. Here they are with the drawing from their record and the stage's sprite patterns; the number is the type.

Stage 0 enemies Stage 1 enemies Stage 2 enemies Stage 3 enemies Stage 4 enemies Stage 5 enemies Stage 6 enemies Stage 7 enemies Interior enemies

The character objects are part of the map: hatches, turning heads, towers that release enemies. Each class has its shapes (p15:B661):

Class 9, stage 1 Class 1, stage 2 Class 7, stage 5 Class 16, stage 4

The bosses

There are five (0xE340), each with its 10-byte record (p09:BB01), its box and its core. Boss 1 fires six bullets in a fan. Boss 2 charges and releases four-sprite enemies. Boss 3 throws growing tongues. Boss 4 releases beams. Boss 5 is ten pieces that come out two at a time.

Boss 1 Boss 2 Boss 3 Boss 4 Boss 5

When one is beaten, its mouth stays open for 300 frames (p11:A93F). If the ship goes in, it reaches the interior; if not, the boss blows up and there is no interior.

The interior

It has a core of 24 hits (p02:8570). When the ship passes its X the 13-step ending starts (p01:74A2), with YOU CAPTURED. The prize depends on how many frames the boss fight lasted (p02:9218): under 300, two weapons; under 900, one; otherwise, NOTHING.

Two weapons One weapon None

The ship and the power meter

The red capsules move the lit box of the power meter, and the other button uses it (p01:7D4F). The meter has more or fewer boxes depending on the captured weapons (p02:8060). The seven that can be captured, in order, are UP LASER, DOWN LASER, NAPALM MISSILE, REFLEX RING, EXTEND LASER, BACK BEAM and FIRE BLASTER. The shield takes 10 hits, and the blue capsule destroys every enemy on the screen.

The ship

The 25 power meter labels (p14:9BD3):

The labels

The special capsules appear on the map and last 15 seconds (p02:9034). With D.VARRIOR the options circle the ship; R.DRILL turns the ship into a drill that breaks walls; E.SLOW makes the enemies move every other frame; VECTOR changes the shot.

The capsules

From left to right: the power meter one (0x29), the one that destroys everything (0x2A), the extra life (0x2B), the two point ones (0x2C and 0x2D), and D.VARRIOR, R.DRILL, E.SLOW and VECTOR.