Aurorus Magnum, the Sword of Frigidum

Beyond Powerful. Aurorus Magnum, the Sword of Frigidum, is one half of one of the four Daemon Lords, children of the Demon King Frigidum. Due to this terrifying power, Aurorus Magnum' stats go beyond 30, leading to them being the following.
Strength: 31 (+10) [Save: +10]
Dexterity: 22 (+6) [Save: +6]
Constitution: 35 (+12) [Save: +12]
Intelligence: 23 (+6) [Save: +14]
Wisdom: 21 (+5) [Save: +5]
Charisma: 13 (+1) [Save: +9]

Legendary Resistance (3/Day). If Aurorus Magnum fails a saving throw, he can choose to succeed instead.

Colossal. Aurorus Magnum is a size Colossal. It takes up a 7 by 7 space.

Aura of the Frozen Sword. Entering the Aura around Aurorus Magnum causes a creature to take 10 Cold damage. Staying in it will increased it by 10 each turn the creature is in the aura, and this stacks until the creature dies.

Banishment.  When Aurorus Magnum drops to 0 hit points, his body explodes into snowflakes. As long as Frigidum, the Demon King, is still alive, Aurorus Magnum can reform even when killed in Cocytus.

Cold Absorption. Whenever Aurorus Magnum is subjected to cold damage, he takes no damage and instead regains a number of hit points equal to the cold damage dealt.

Magic Resistance. Aurorus Magnum has advantage on saving throws against spells and other magical effects.

Regeneration. Aurous Magnum regains 25 hit points at the start of each of his turns.

Frozen Chill. Aurorus Magnum can go through physical objects, ending his turn in that space does not do damage, but does force him to go half speed next turn.

Tunneler. Aurorus Magnum can burrow through solid rock at half his burrow speed and leaves a 25-foot-diameter tunnel in his wake.

Flyby. Aurorus Magnum doesn't provoke opportunity attacks when he flies out of an enemy's reach.

Siege Monster. Aurorus Magnum deals double damage to objects and structures.

Ice Walk. Aurorus Magnum can move across and climb icy surfaces without needing to make an ability check. Additionally, difficult terrain composed of ice or snow doesn't cost him extra movement.

Multiattack. Aurorus Magnum can use its Frightful Presence. It then makes four attacks. Two with its Bite, and two with its Slam. If it has someone in its mouth, then it can also preform a swallow.

Bite. Melee Weapon Attack: +18 to hit, reach 20 ft., 1 target. Hit: 49 (6d12 + 10) Piercing damage, plus 25 Cold damage.
If the target is Huge or smaller size, it must succeed on a DC 28 Dexterity Saving throw or be stuck in the mouth.

Slam. Melee Weapon Attack: +18 to hit, reach 25 ft., 1 target. Hit: 41 (7d8 + 10) Bludgeoning damage, plus 25 Cold damage.
A target hit must also pass a DC 28 Constitution saving throw or be knocked prone and stunned until the end of their next turn. On a pass, the target is only knocked prone.

Tail. Melee Weapon Attack: +18 to hit, reach 15 ft., 1 target. Hit: 32 (5d8 + 10) Bludgeoning damage, plus 25 Cold damage.

Frightful Presence. Each creature of Aurorus Magnum that is within 120 feet of him and aware of him must succeed on a DC 28 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the Aurorus Magnum's Frightful Presence for the next 24 hours.

Cold Breath (Recharge 5-6). Aurorus Magnum exhales an icy blast in a 90 foot cone. Each creature in that area must make a DC 28 Constitution saving throw, taking 108 (24d8) Cold damage on a failed save, or half as much damage on a successful one.

Swallow. The opponent who has been bitten must make a DC 30 Dexterity Saving throw or will be swallowed by Aurorus Magnum. A swallowed creature is blinded and restrained, it has total cover against attacks and other effects outside Aurorus Magnum, and it takes 63 (18d6) acid damage at the start of each Aurorus Magnum's turns. If he takes 50 damage or more on a single turn from a creature inside him, he must succeed on a DC 19 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of Aurorus Magnum. If he dies, a swallowed creature is no longer restrained by him and can escape from the corpse by using 20 feet of movement, exiting prone.

Summon Demon (1/Day). Aurorus Magnum magically summons 1d6+2 Frigid Maw's.

Aurorus Magnum 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. Aurorus Magnum regains spent legendary actions at the start of his turn.

Detect (Costs 1 Action). Aurorus Magnum makes a Wisdom (Perception) check.

Tail Attack (Costs 1 Action). Aurorus Magnum makes a Tail attack.

Move (Costs 1 Action). Aurorus Magnum moves up to half his speed.

Chomp (Costs 2 Actions). Aurorus Magnum makes one Bite attack, or uses his Swallow.

Frozen Treat (Costs 2 Actions). If anyone is inside of Aurorus Magnum, he will spit out the person, and regain any HP that they lost while inside.

Charge (Costs 3 Actions). Aurorus Magnum charges foreword in a straight line. Anyone in Aurorus' path must make a DC 28 Dexterity Saving Throw. On a fail, they are hit by two Slam attacks and pushed back 30 feet and knocked prone.

If Aurorus Magnum, the Sword of Frigidum is fighting along side Frigis Bael, the Shield of Frigidum, if either one drops to below 10% of their Max Hit Points, one will flee the battle. Once the other also drops to below 10% of their Max Hit Points, the two will fuse into the powerful fiend known as Aion, the Eternal Aegis of Frigidum.