Adult Ice Skeleton

Legendary Resistance (3/Day). If the Adult Ice Skeleton fails a saving throw, it can choose to succeed instead.

Multiattack. The Adult Ice Skeleton makes three attacks with his Ice Rapier.

Ice Rapier. Melee Weapon Attack, +13 to hit, reach 5 ft., one target. Hit 24 (1d8 + 8) piercing damage and  (4d6) ice damage.

Ice spells (Recharge 5-6). The Adult ice Skeleton can replace his action with one of these spells:
Cone of Cold at level 6
Ice Knife at level  6
Ice Storm at level 5

Icy step. Briefly surrounded by silvery-Icy mist, teleport up to 30 feet to an unoccupied space the Adult ice Skeleton can see.

Icy block. If an enemy creature hits this creature with any melee attack, using it's reaction the shield of the Adult Ice Skeleton grows spikes dealing 10 (1d8) piercing damage and (2d6) Ice damage

The Adult Ice Skeleton can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Adult Ice Skeleton regains spent legendary actions at the start of its turn.

Ice chain. Melee Weapon Attack, +13 to hit, reach 30 ft., one target. Hit  25 (1d10 + 8) piercing damage and (4d6) Ice damage.

Ice Rapier. The Adult Ice Skeleton makes an Ice Rapier attack

Ice Bash. The Adult Ice Skeleton bashes his shield against any target within 5 ft. if the target fails the strenght contest they fall prone.