The Mountain Sire is a treant boss. At the lowest Threat it has 1350 health, hits for 24 and carries 12 armor; the uber version you meet in the Mortal Arena has ×3 the health and ×1.75 the damage. You need Sire's Heartstone to call it out.

It waits at the end of Cragmaw Deep, in place of Imp Overlord, and belongs to Demon Gate.

Every kill rolls its list twice. 8 Uniques sit on it: four ordinary ones splitting 90.0% of it between them, and four Exceptional ones splitting the last 10.0%, which puts any one of those at about 1 in 40 of what it gives up. The Exceptional ones are Bedrock Testament, The Mountain Sire's Spine, Sediment and The Landslide Clause.

It fights with Seismic Slam, Rockfall, Stone Bulwark and Mountain Wakes, and changes phase at 55% health.

It calls in Rubble Roller.