Raremetalfoes Bismugear

Fullmetalfoes Alkahest

Metalfoes Mithrilium

Fullmetalfoes Fusion

These suggests that the rarities for Raremetalfoes Bismugear and Fullmetalfoes Fusion might be Common or Super Rare, Metalfoes Mithrilium might be Ultra Rare, and Fullmetalfoes Alkahest might be Secret Rare.

Source: https://yugiohblog.konami.com/articles/?p=7998