Ossuary
While you have at least 5 Bone Shield charges, the cost of Death Strike is reduced by 5 Runic Power. Additionally, your maximum Runic Power is increased by 10.
Tree position
In the Blood Death Knight talent tree, Ossuary sits in the Blood specialization talents, row 4 of 11. It is a single-point node.
Connected above
The tree draws a line into Ossuary from Vampiric Blood.
Vampiric BloodEmbrace your undeath, increasing your maximum health by 30% and increasing all healing and absorbs received by 30% for 10 sec.
Connected below
Ossuary leads on to Leeching Strike, Heartbreaker and Foul Bulwark.

HeartbreakerYour Heart Strike generates 2 additional Runic Power per target hit.
Foul BulwarkEach charge of Bone Shield increases your maximum health.
Same row
Also on this row: Improved Vampiric Blood, Improved Heart Strike and Relish in Blood.
Improved Vampiric Blood2 ranksVampiric Blood's healing and absorb amount is increased by 5% and duration by 2 sec.

Relish in BloodWhile Crimson Scourge is active, your next Death and Decay heals you for (37.5% of Attack Power) health per Bone Shield charge and you immediately gain 10 Runic Power.
Talent trees
Ossuary is in the talent tree of 3 specializations. Death Knight: Blood (Tank), Frost (DPS), Unholy (DPS).
Ossuary Changes by patch
Tracked changes to this talent between game data builds, newest first.
- First tracked in the game data (patch 12.1.0)