Scales of Mourning
From RoR Wiki
Scales of Mourning is a Tome of Knowledge Bestiary entry for the Basilik.
Order & Destruction Instructions
Find and kill the Basilik 'Stinky' (this mob is not a champion) in his cave in the northwestern corner of Black Crag at Sulfur Cave (loc 5k, 8k).
Be sure to be the only one damaging him to get the unlock
Killing the level 39 Champion basilisk (loc 41k, 38k) also gives this unlock.
Rewards
Item: Beastial Tactic Fragment
XP: 1476