The tune played on the title screen is The Blue Danube by Johann Strauss II. The tune played during gameplay is In the Hall of the Mountain King by Edvard Grieg.
Taking a BREAK
The game quits if BREAK - that is, CAPS SHIFT and SPACE - is pressed (see 87F1).
If you type the digits 6031769 at any point during the game, a cheat mode is activated that enables Willy to teleport to any cavern; a boot appears next to Willy's remaining lives to show that the cheat mode has been activated.
For example, to teleport to The Vat, hold down keys '2' and '3', and then press '6' to activate the teleporter. For a list of all the caverns and their teleport codes, see the Caverns page.
The number 6031769 comes from Matthew Smith's driving licence, "with an error in it and twisted round a bit" (as he put it in an interview for issue 48 of Retro Gamer magazine).
Stuck on 16
In The Sixteenth Cavern, Willy can get stuck if he enters the area below the portal before collecting all the items outside that area:
If that happens, he will have to wait until the air runs out before getting a second chance to escape from the cavern.
See also No way out of The Warehouse.
No swordfish for cheats
The game ending - with Willy above ground and the portal in The Final Barrier changed to the swordfish graphic - is not shown if cheat mode is activated (see 9037).
Unused crumbling floor
The crumbling floor tile in Skylab Landing Bay is unique to that cavern, and also not used.
To place a couple of these tiles in the cavern in order to see them crumble:
POKE 58811,10: POKE 58812,10: POKE 58930,10
Unused conveyors
Every cavern definition contains a conveyor definition, and every conveyor has non-zero length and is animated by the routine at 9105. But there are two caverns in which the conveyor is hidden or otherwise unusable.
The first unused conveyor is of length 1, defined at (0,19) in The Endorian Forest (see D66F). Instead of a conveyor, the space is occupied by a background tile.
To show the conveyor:
POKE 54291,67
The other unused conveyor is of length 3, defined at (9,7) in Amoebatrons' Revenge (see F66F). Instead of a conveyor, the space is occupied by a platform, whose third row of pixels is animated as if it were a conveyor (which is a bug).
To replace the platform with conveyor tiles:
POKE 62759,4: POKE 62760,4: POKE 62761,4
Note that this conveyor moves left to right, and so if it were activated it would make the cavern unfinishable. To make the conveyor move right to left:
POKE 63087,0
The persistent item
The item below the portal in The Sixteenth Cavern does not disappear if Willy leaves it till last and collects it by falling on it from above. The reason for this is that the portal is opened as soon as Willy collects the item, and the screen is not refreshed before he moves on to the next cavern.
Light logic
At times it might seem as if the light beam in Solar Power Generator moves around at random, but in fact its movements are predictable and always follow these simple rules (see 8D73):
In addition, for every frame that the light beam is in contact with Willy, the air supply is reduced by an extra eight or twelve units - four for each of the two or three cells of Willy's sprite that the beam touches - making nine or thirteen units in total. For every eight units of air consumed, one vertical line of pixels is removed from the right end of the air bar (see 8A3C).
Top half twice
When The Final Barrier is drawn to the screen buffer at 7000, the graphic data for the top half of the cavern (at A000) is copied twice: once after the first (pointless) run through the loop at 8A8C, and again after the second run through the loop has drawn the bottom half of the cavern.
Bottom half twice
After Willy has jumped through the portal in The Final Barrier to the ground above, and the celebratory sound effect and colour-cycling effect have finished, the bottom half of Willy's sprite can be been dangling below the swordfish graphic (where the portal was) while the remaining air supply decreases to zero.
This happens because the section of code at 903E draws Willy above ground, but does not remove him from the portal entrance. And although his residual bottom half is hidden briefly by setting the appropriate attribute values to 0 (INK 0: PAPER 0), it is left on display with an attribute value of 1 (INK 1: PAPER 0) after the colour-cycling effect has finished.
Item graphics
The commonest item graphic is the key, which appears in Central Cavern, The Menagerie, Abandoned Uranium Workings, Processing Plant, The Vat, Wacky Amoebatrons, The Warehouse, Amoebatrons' Revenge, Solar Power Generator and The Final Barrier.
Next is the banana, which appears in Miner Willy meets the Kong Beast and Return of the Alien Kong Beast:
The other eight caverns have their own unique item graphics:
Item counts
Thirteen of the twenty caverns have a full set of five items.
Miner Willy meets the Kong Beast, Skylab Landing Bay and The Sixteenth Cavern each have four items.
The Bank and Solar Power Generator both have three items.
There are no caverns that have exactly two items.
Wacky Amoebatrons and Amoebatrons' Revenge both have only one item.
Extra items
The Bank has five items defined, but only three of them are used; The Sixteenth Cavern also has five items defined, but only four of them are used.
The two extra items in The Bank are at (6,19) and (13,30), shown here in bright white:
The extra item in The Sixteenth Cavern is at (5,26) - in the path of the cyan guardian - shown here in bright white:
The fastest guardians
There are three guardians that move four pixels up or down every frame - faster than any other guardians in the game: the white Skylab in Skylab Landing Bay, the magenta guardian in The Warehouse, and the cyan guardian in Amoebatrons' Revenge.
Guardian colours
The most common guardian colour is yellow (21 instances), and the least common colour is black (only one instance, in Eugene's Lair).
As for the other colours, there are 3 blue guardians, 10 red guardians, 12 magenta guardians, 13 green guardians, 14 cyan guardians, and 5 white guardians.
Guardian counts
The cavern with the most guardians is Amoebatrons' Revenge, which has eight (the maximum).
The cavern with the least guardians is Central Cavern, which has only one.
Guardians need a clear path
The guardian-drawing code kills Willy if a guardian collides with anything that's already been drawn in the cavern. This means, for example, that Willy is killed if a guardian hits a nasty, a wall or the floor.
See this happen by placing a wall block in the path of the guardian in Central Cavern:
POKE 45327,22
Off on the wrong foot
In some caverns, Willy starts off facing the wall, and so has to turn round before navigating his way out:
To make Willy start off facing the other way:
Variable air supply
The initial air supply varies from cavern to cavern by small amounts, because of differences in the initial value of the game clock at 80BD - 0x80, 0xF0, 0xF8 or 0xFC - which is copied from byte 0x02BD of the cavern definition.
The caverns with the greatest initial air supply are Central Cavern, The Cold Room, Ore Refinery, The Bank and The Final Barrier, which initialise the game clock to 0xFC.
Next are The Endorian Forest, Skylab Landing Bay and The Sixteenth Cavern, which initialise the game clock to 0xF8.
Then it's Solar Power Generator, which initialises the game clock to 0xF0.
The other 11 caverns initialise the game clock to 0x80, which means the cell at the right end of the air bar in those caverns starts off with only three white pixel columns instead of seven.
Repeating caverns
There are six caverns in which the guardians all return to their original locations at the same time at least once before the air runs out:
Note that normal speed horizontal guardians are not drawn to the screen at their initial locations when Willy enters a cavern, because they are moved once before the cavern is first drawn; the same is true for each vertical guardian, unless its initial position is at the top of its path and it is initially moving up, or its initial position is at the bottom of its path and it is initially moving down - in these cases it remains stationary for one frame before changing direction.
No way out of The Warehouse
If too many of the crumbling floors have disappeared in The Warehouse, Willy won't be able to reach the portal. For example:
If that happens, he will have to wait until the air runs out before getting a second chance to escape from the cavern.
See also Stuck on 16.
The unreachable million
The score (at least, the part of it that is printed - see 8425) rolls around to zero when it hits a million.
Horizontal Skylabs?
There are three horizontal guardians defined in Skylab Landing Bay, but they're not used. We can only wonder what they might have looked like before being replaced by the Skylabs.
Out of bounds
There are two vertical guardians that start off in a location that they never return to.
The first one is the bright magenta guardian in The Warehouse. It starts off at pixel y-coordinate 0 - the very top of the cavern - but does not go above y=4 again after it has started moving (see F2F2).
The second one is the blue vertical guardian in Solar Power Generator. It starts off at pixel y-coordinate 80 - touching the platform that Willy is standing on initially - but does not go below y=79 again after it has started moving (see FAEB).
Source code remnants
Before the game starts for the first time, the 512-byte cavern buffer at 8000 contains source code remnants (shown below). The DB directives define part of the title screen tune data at 846E. There are more source code remnants at 934C.
8000 DEFM "50,171,192,50,48,68"
8013 DEFW $0316 790 DB "50,48,68,50,171,192,50,136,137"
8015 DEFB $22
8016 DEFM $09,"DB",$09,"50,48,68,50,171,192,50,136,137"
8038 DEFW $0320 800 DB "50,136,137,50,114,115,50,76,77"
803A DEFB $22
803B DEFM $09,"DB",$09,"50,136,137,50,114,115,50,76,77"
805D DEFW $032A 810 DB "50,7?????????????92,50,38,48"
805F DEFB $20
8060 DEFM $09,"DB",$09,"50,7"
8068 DEFB $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
8075 DEFM "92,50,38,48"
8080 DEFW $0334 820 DB "50,38,4??50,171,192,50,48,68"
8082 DEFB $20
8083 DEFM $09,"DB",$09,"50,38,4"
808E DEFB $FF,$00
8090 DEFM "50,171,192,50,48,68"
80A3 DEFW $033E 830 DB "50,48,????0,171,19??50,136,137"
80A5 DEFB $22
80A6 DEFM $09,"DB",$09,"50,48,"
80B0 DEFB $00,$00,$00,$00
80B4 DEFM "0,171,19"
80BC DEFB $00,$00
80BE DEFM "50,136,137"
80C8 DEFW $0348 840 DB "50,136,137,???114,115,50,76,77"
80CA DEFB $22
80CB DEFM $09,"DB",$09,"50,136,137,"
80DA DEFB $FF,$00,$00
80DD DEFM "114,115,50,76,77"
80ED DEFW $0352 850 ?B "50,76,77,50,171,203,50,38,51"
80EF DEFB $20
80F0 DEFM $09,$FF,"B",$09,"50,76,77,50,171,203,50,38,51"
8110 DEFW $035C 860 DB "50,38,51,50,171,203,50,51,64"
8112 DEFB $20
8113 DEFM $09,"DB",$09
8117 DEFM "50,38,51,50,171,203,50,51,64"
8133 DEFW $0366 870 DB "50,51,64,50,171,203,50,128,129"
8135 DEFB $22
8136 DEFM $09,"DB",$09,"50,51,64,50,171,203,50,128,129"
8158 DEFW $0370 880 DB "50,128,129,50,102,103,50,86,87"
815A DEFB $22
815B DEFM $09,"DB",$09,"50,128,129,50,102,103,50,86,87"
817D DEFW $037A 890 DB "50,64,65,50,128,171,50,32,43"
817F DEFB $20
8180 DEFM $09,"DB",$09,"50,64,65,50,128,171,50,32,43"
81A0 DEFW $0384 900 DB "50,32,43,50,128,171,50,43,51"
81A2 DEFB $20
81A3 DEFM $09,"DB",$09,"50,32,43,50,128,171,50,43,51"
81C3 DEFW $038E 910 DB "50,43,51,50,128,171,50,128,129"
81C5 DEFB $22
81C6 DEFM $09,"DB",$09,"50,43,51,50,128,171,50,128,129"
81E8 DEFW $0398 920 DB "50,128,129,50,102............."
81EA DEFB $22
81EB DEFM $09,"DB",$09,"50,128,129,50,102"