For a crossbow in Mabinogi, the Erg expansion materials shown by the wiki are:

  • Level 5: Iron Ingots x20, Iron Plates x5, Holy Mineral Fragment x3, Ancient Monster Core x1, Handicraft Tools, Crossbow.
  • Level 10: Gold Ingots x20, Gold Plates x5, Holy Mineral Fragment x3, Ancient Monster Core x3, Ring accessory, R1+ Shuriken. The crossbow page notes crossbows follow the bow/crossbow Erg category, and the Erg materials page lists the shared weapon-type requirements.

The crossbow also has its own Erg bonus page, which confirms it is a separate Erg weapon category.

Materials

If you mean the Erg sacrifice materials specifically, the common materials for the bow/crossbow category are listed on the Erg materials page, and the exact item set changes by Erg rank.

Note

Some community guides list the crossbow category together with bows, so make sure you’re looking at the bow/crossbow section rather than a different weapon type.

TL;DR: crossbow Erg uses the bow/crossbow material table; the commonly cited opening materials are Iron Ingots, Iron Plates, Holy Mineral Fragment, Ancient Monster Core, Handicraft Tools, and a Crossbow for the first listed stage.