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The eye-catcher animation coded in the BIOS comprises both sprites and FIX layer tiles. The graphics data for both must be provided in the cartridge sprite and FIX ROM images.

The revolving NEO.GEO graphic consists of sprites (TBD).

The "MAX 330 MEGA" & "PRO-GEAR SPEC" text as seen on smaller/early-release cartridges (eg. Puzzle De Pon) comprises FIX-layer tiles. The tiles used are defined in the BIOS ROM @$C1F34A. Each line of text is itself two (2) FIX-layer tiles high, and is animated using a 'wipe in' effect from left-to-right to render each line in turn. These are the tiles used to display each line of text:

static const uint16_t max_330_mega[2][15] =
  { 0x05, 0x07, 0x09, 0x0B, 0x0D, 0x0F, 0x15, 0x17, 0x19, 0x1B, 0x1D, 0x1F, 0x5E, 0x60, 0x7D },
  { 0x06, 0x08, 0x0A, 0x0C, 0x0E, 0x14, 0x16, 0x18, 0x1A, 0x1C, 0x1E, 0x40, 0x5F, 0x7C, 0x7E }
static const uint16_t pro_gear_spec[2][17] =
  { 0x7F, 0x9A, 0x9C, 0x9E, 0xFF, 0xBB, 0xBD, 0xBF, 0xDA, 0xDC, 0xDE, 0xFA, 0xFC, 0x100, 0x102, 0x104, 0x106 },
  { 0x99, 0x9B, 0x9D, 0x9F, 0xBA, 0xBC, 0xBE, 0xD9, 0xDB, 0xDD, 0xDF, 0xFB, 0xFD, 0x101, 0x103, 0x105, 0x107 }

Both the revolving logo and the FIX-layer text utilise palette #15. For the revolving logo, the palette is updated on-the-fly (from data stored in the BIOS ROM @$C1F03E) to implement the fade effect.

Before the FIX-layer text is displayed, the following data is written to palette #15:

static const uint16_t eye_catcher_pal[] = 
  0x0000, 0x0fff, 0x0ddd, 0x0aaa, 0x7555, 0x0000, 0x0000, 0x0000,
  0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000

SNK Logo consists of (TBD)

It would be possible, then, by replacing the FIX-layer tile data for the above tiles with alternate text/graphics to create a somewhat customised eye catcher without requiring a custom eye-catcher routine in the game cartridge itself.