Arctic Aries

Cold Aura. While it's alive, the arctic aries generates an aura of bitter cold that fills the area within 10 feet of it. At the start of the arcitc aries turn, all nonmagical flames in the aura are extinguished. Any creature that starts its turn within 10 feet of the arctic aries takes 10 (3d6) cold damage.

Innate Spellcasting. The arcitc aries' innate spellcasting ability is Wisdom (spell save DC 17). The arctic aries can innately cast the following spells, requiring no material components:

At will: Frostbite (3d6)
2/day: Ice Storm
1/day: Wall of Ice

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

Trampling Charge: If the arctic aries moves at least 20 feat straight toward a target and then hits it with a ram attack on the same turn, the target takes an extra 3d8 bludgeoning damage. If the target is a creature, it must succeed on a DC 17 Strength saving throw or be knocked prone. If the targeet is prone, the arcitc aries can make another stomp attack against it as a bonus action. 

Sure-Footed: The arctic aries has advantage on Strength and Dexterity saving throws made against effects that would knock it prone. 

Multiattack. The arctic aries makes two attacks, either one ram and one stomp attack or two stomp attacks. 

Ram. Melee Weapon Attack: + 11 to hit, reach 5 ft., one target. Hit: 30 (5d8 + 7) Bludgeoning damage plus 10 (3d6) cold damge.

Stomp. Melee Weapon Attack: + 11 to hit, reach 10ft., one target. Hit:  21 (4d6+7) bludgeoning damage plus 10 (3d6) cold damge. 

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

Move . The arctic aries can move up to it's speed.

Ram (Costs 2 Action). The arctic aries can make one ram attack.

Stomp. The arctic aries can make one stomp attack.