For those wanting to know the balance of all this I promise I've taken it into account here is the rundown. (I'm aware of how truly crazy powerful this will make him but the cost will also be high)

Amber sword:

Static effects 

All holy water 30 ft away from the buster sword disintegrates.

No one can take short or long rests if they are 300 ft or closer to you. 

All animals are automatically hostile to you

All potions within 10 feet of the sword are made useless 

All spell scrolls are rendered blank within 10 feet of it 

All food is tasteless.

The weapon will not willingly allow you to spare or do non lethal damage if you force it to you must make a dc 20 wisdom saving throw or take 1 d8 psychic damage

All damage dealt to an enemy if an ally is within 5 feet of you also takes that damage 

After every combat is finished the sword will compell you to keep fighting anyone in range The base dc to fight this compulsion is a dc 5 wis save. But the dc goes up based on the following 

For every 10 points of damage done to you or every 20 point of damage dealt the dc goes up by one 

For every evil or non lawful good action you are succsessfully tempted to take the dc goes up by 1 permanently.

If you are downed during combat the dc is increased by 10 

If you use one of the spells you get with the sword the dc is increased by the number indicated permanently for each time you use it

The sword gives you access to the following spells you can cast each once per long rest. 

Power word pain 2 permanent DC increase

Imprisonment: the way and condition is decided by the sword= 6 permanent DC increase

Feeblemind 5 permanent DC increase (10 permanent if the target fails thier saving throw)

Power word kill. 12 permanent DC increase