Bomberman 64 (U):

80225A74 main game loop (the branch, specifically)
802259F4 main game loop (first jal)
800655F8 copyright screen wait timer (and seemingly has other uses)
    $12C gets written by 80238DDC (generic?)
    start of function: 80238D98
    wrapper function: 8023900C
    calls where A0 (frame time) > 1:
        RA: 800434B4 (A0=$14)
        RA: 8004356C (A0=$12C)
    A0=$12C is set at 80043568, so change that to 1 and...

decomp routine struct: 8014B808
LW ($4) might be ROM offset?
LW ($8) is current offset into compressed file?
rom$162008 start of compressed file?
rom$160000 points to that start (confirmed, it adds 0x00160000 from A2 at 80226758)
rom$163B62 start of second file (again, starts with decomp length)
    breakpoint at 80292C90 to only see raw bytes being written (in V0)
    for compression format details, refer to:
    https://github.com/PartyPlanner64/PartyPlanner64/wiki/Compression#compression-type-1
ring-buffer?: 80305000

seems like the rom is split into 0x20000 chunks (128 KiB, 1 megabit)
first chunk is at 0x120000?
err wait, that doesn't work for 0x200000; it's 0x40000 long!

anyway back at the rom:$160000
let's tear apart this header.
it's entirely s32s, so that's simple enough.
first word: $00002008
this is the offset from this position into the first (compressed) file.
next: $00000400
not sure what this is. number of entries in this header? always seems to be 0x400.
next: $00000000
offset to first file. added to the initial 0x2008.
next: $00000016
size of first file.
next: $00000016
offset of second file. added to the initial 0x2008.
next: $00001B44
this is the compressed size of the second file.
next: the rest of the entries follow this pattern of (offset, size).
(except $FFFFFFFF means no file)

now what's the data at rom$162008?
first byte: $09
i think this is the number of entries in this sub-header,
except it's not. maybe it indicates the type of something?

rom$162008:
09
00 20 01
00 21 02
00 23 03
00 25 04
00 26 05
00 1F 06
00 22 07
00 00 2F 80

rom$182008:
0A
00 28 01
00 29 02
00 2A 03
00 2B 04
00 2C 05
00 2D 06
00 2E 07
00 2F 08
00 30 09
00 31 0A
00 (halfword padding?)
00 00 79 80

rom$1A2008:
07
00 38 01
00 39 02
00 3A 03
00 3B 04
00 3C 05
00 3D 06
00 3E 07