The boggard chieftain stood out from the rest of Xanos' creations. It's severed head floated above it's shoulders as a blackened cloud of airborne cinders in a roughly frog-skull shape. Flames flickered in it's eyes. Pale ash swirled through the bones below forming the rough shape of what it's body looked like in life, brawney, wide and powerful.
As the body walked forward with an unnatural fluid grace the head seemed to take an extra moment to move with it. The cinder skull bobbed and floated to catch up. Occasionally it completely discorporated into a cloud of scorching cinders that flared to burning life, swept up the grey ash into a conflagration and churned around the animated body before snapping back into the shape of a skull again moments later.
This thing is technically two creatures. A Flaming Swarm Beheaded floating above a Bloody Burning Skeleton. It's a CR 2 creature and a CR 3 creature. It's also kind of a glass cannon. Super nasty in melee, but will probably go down to the very first blast of AoE we run across.