Caladbolg

Cannot be auctioned, traded, bazaared, or delivered.
Cannot be obtained as a random reward from the Gobbie Mystery Box Special Dial and similar sources.

Caladbolg: Caladbolg, sometimes written Caladcholg ("hard blade"), is the sword of Fergus mac Róich from the Ulster Cycle of Irish mythology. Spelled Caladcholg, it is also associated with the more obscure Ulster hero Fergus mac Léti, suggesting a conflation of two legends. It was said to be a two-handed sword that made a circle like an arc of rainbow when swung, and to have the power to slice the tops off hills and slaughter an entire army. (Wikipedia)