Innate Spellcasting. The aatxe's innate spellcasting ability is Wisdom (spell save DC 16, +8 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At will: detect evil and good, detect magic, alter self, fire shield

4/day each: wall of fire, flame strike

2/day each: plane shift, fire storm

Magic Resistance. The aatxe has advantage on saving throws against spells and other magical effects.

Reckless. At the start of its turn, the aatxe can gain advantage on all melee weapon attack rolls it makes during that turn, but attack rolls against it have advantage until the start of its next turn.

Charge. If the aatxe moves at least 10 feet straight toward a target and then hits it with a gore attack on the same turn, the target takes an extra 9 (2d8) piercing damage. If the target is a creature, it must succeed on a DC 19 Strength saving throw or be pushed up to 10 feet away and knocked prone.

Multiattack. The aatxe makes three smash attacks. Up to two of these attacks can be replaced by Gore.

Gore. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 18 (2d8 + 9) piercing damage. If the target is a Medium or smaller creature, must succeed on a DC 16 Constitution saving throw or it has disadventage on DEX, STR and CON saving throws until target's next turn.

Smash. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 19 (3d6 + 9) bludgeoning damage.

Obliterate. Aatxe moves 25 ft  in a straight line, breaking through all the creatures that are in its path. Each creature that was in its way, must make a Dextery saving throw, CD 19. On a failed save, a creature will be knocked prone and takes 17 (2d6 + 10), or half as much damage on a successful one.

Mari's Blessing. Once per turn, when a creature that the Aatxe can see hits it with an attack, it can use its reaction to halve the attack's damage 

Aatxe 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. Aatxe regains spent legendary actions at the start of her turn.

Smash (1 action). Aatxe makes a Smash attack.

Earthquake (2 actions). Each creature in a 15-foot-radius sphere centered on that point must make a Dexterity saving throw. A target takes 4d6 force damage on a failed save, or half as much damage on a successful one.

Heaven's Roar (3 actions). Aatxe creates a bolt of lightning that arcs toward a target of its choice that aatxe can see within range. Three bolts then leap from that target to as many as three other targets, each of which must be within 30 feet of the first target. A target can be a creature or an object and can be targeted by only one of the bolts. A target must make a Dexterity saving throw, CD 14. The target takes 10d8 lightning damage on a failed save, or half as much damage on a successful one.