In dragon form , His scales are coded in anti magic granting him immunity to all spells 6th lvl and lower  

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

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 42(4d20 + 40) piercing damage plus 30(6d10) force damage.

Claw. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 25(4d12 + 40) slashing damage.

Tail. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 25 (2d10 + 40) bludgeoning damage.

Arcane Dragon's Eruption: Acnologia raises his hand and erupts a blast of Magic beneath his opponent. 63 (18d6) force damage 

Arcane Dragon's Flash: Acnologia raises his finger and fires a giant blast of Magic at his opponents.63 (18d6) force damage

Arcane Dragon's Breath: Acnologia opens his mouth and fires off numerous explosions. 63 (18d6) force damage

Arcane Dragon's Explosion: Acnologia exerts his Magic omnidirectionally, causing a huge explosion. 63 (18d6) force damage

Eternal Flare: Acnologia casts starry lights in the sky, which rain down in a massive radius as beams with an intense destructive force that create huge explosions on impact.

Frightful Presence. Each creature of the dragon’s choice that is within 120 feet of the dragon and aware of it must succeed on a DC 21 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 dragon’s Frightful Presence for the next 24 hours.

Arcane Dragon's Roar: (Recharge 5–6). The dragon exhales fire in a 180-foot cone or 290 foot line and 40ft wide depending on the dm choice. Each creature in that area must make a DC 24 Dexterity saving throw, taking 200(26d10) force damage on a failed save, or half as much damage on a successful one. 

Eternal Flare : Acnologia casts thousands of stars which rain down destruction.(Recharge 5–6). The dragon exhales fire in a 90-foot cone. Each creature in that area must make a DC 24 Dexterity saving throw, taking 91 (26d6) force damage on a failed save, or half as much damage on a successful one.

Power of the End : Acnologia creates a destructive energy blast from the palm of his hand. Each creature in that area must make a DC 21 constitution saving throw, taking 90-foot cone or take 250 force damage 

Time Magic : Acnologia after consuming the Space Between Time was able to wield this Caster Magic. he can stop time and see into the future for up to 5 turns granting anyone who attacks him a disadvantage on attack rolls   

Healing Magic: , Acnologia uses healing magic mass heal himself 2 times per day or his allies 

The dragon 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 dragon regains spent legendary actions at the start of its turn.

Detect. The dragon makes a Wisdom (Perception) check.

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 25 Dexterity saving throw or take 25(2d12 + 40) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

magic eater. When a spell of 6th lvl or lower he can ear it and the damage delt can be added onto his nexted attack or used to heal himself 

Time Magic: After consuming the Space Between Time, Acnologia is able to wield this Caster Magic, which gives him control of space and time. With this power, he could teleport the seven Dragon Slayers into his world with a Rift in Space and Time. By warping the Dragon Slayers into his world, he could trap them in crystal-like pillars that allow him to balance his own Magic Power. wisdom saving throw  of 22 or get teleported between time and frozen and he can use there skills. only way too free people is wish or kill Acnologia