Circle of Glasty Flames-Once a creature enters the space of the Giant skeleton they have to make a con saving throw of 23 or take (2d6) flame and (2d10) necrotic.  

Veil of Shadows. Their is a veil of darkness around it 

Multi-Attack. The Giant Skeleton makes two attacks with its Giant Claw and one attack with its rock throw 

Giant Claw. Melee Attack: +15 to hit, reach 5 ft., one target. Hit: 5 (3d10 + 20) piercing damage.

Rock Throw. Ranged Weapon Attack: +15 to hit, range 80/320 ft., one target. Hit: 5 (12d8 + 15) bludgeoning damage.

Cancel shadows It can cancel veil of shadows 

Grab. If a creature misses an attack on the Giant Skeleton as a reaction the skeleton can grab the creature as a strength check. 

3 Legendary Actions 

Extra Attack (cost one legendary action) Giant Skeleton can make one Claw attack 

Legendary resistance