Axe of Sulphurous Destruction

This Axe was forged and imbued with pure Sulphur by Hackthorn Hasselhoth, an eccentric Dwarf with a particular interest in Brimstone. It gives off a powerful smell of Sulphur, giving the wielder disadvantage on Stealth checks. 
The Axe of Sulphurous Destruction has 3 abilities.
The Axe of Sulphurous Destruction has 8 charges.

1) As a Bonus Action, you may speak the command word "Incinerate" to cause the Axe to ignite in black necrotic flames. Until you use a Bonus Action to speak the command word "Extinguish" the flames will continue to burn. Whilst lit the Axe does an extra 1d6 Fire damage and 1d6 Necrotic damage on a hit. When you hit certain levels this damage increases. At 10th level both damage types become 2d6. At 14th level both damage types become 3d6. At 17th level both damage types become 4d6. At 20th level both damage types become 5d6. 

2) Whilst your Axe is ignited, you can expend one charge to use your Action to send forth a streak of necrotic fire in a 30ft cone. Anyone in the cone must make a Dexterity saving throw. On a failed save, a creature takes 3d6 Fire damage and 3d6 Necrotic damage. A creature takes half as much on a successful save. The DC for this save is 8 + your Barbarian level halved.

3) Whilst your Axe is ignited, you can expend 3 charges to cast the Brimstone's Fury spell at 3rd level. You may expend additional charges to upcast this up to a maximum of 5th level.
Brimstone's Fury:
When you cast this spell, heated shadowy energy erupts from a point of your choice within 150ft in a 20ft radius sphere. The area gives off a strong smell of sulphur which makes it difficult to breathe within the area. Each creature in it's area must make a Constitution save equal to 8 + Proficiency Bonus + your Constitution modifier. On a failed save a creature takes 4d6 Necrotic damage and 2d6 Fire damage and must make a second Constitution save to avoid being poisoned for 1d8 rounds using the same DC. On a successful save a creature takes half damage and does not need to make the second save. 
At higher levels the damage increases by 1d6 of each type per level. e.g. 5d6 Necrotic and 3d6 fire at 4th level, and 6d6 Necrotic and 4d6 Fire damage at 5th level.

If all charges are expended, roll on the Wild Magic tables. Charges reset on a Long Rest.

Proficiency with a Battleaxe allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Damage: Fire, Damage: Necrotic, Disadvantage: Stealth, Barbarian. You must spend one hour holding and concentrating on the Axe of Sulphurous Destruction. , Versatile, Topple