Introduced in the very first Xenoblade Chronicles game, Unique Monsters are a staple of the series, represented as powerful monsters for players to try and take down for added challenge.
Tenebrous Muramasa is a Unique Monster that appears in Xenoblade Chronicles 3: Future Connected. It can be found only at night, on the Ruined Anti-Air Battery 3 in Yesterdale and defeating it counts towards completing your Enemypaedia.
Tenebrous Muramasa (Level 39) | Yesterdale
For assistance with finding all Unique Monsters in Yesterdale, why not check out our useful guide below:
[Guide] Yesterdale Unique Monsters | Xenoblade Chronicles 3: Future Redeemed