How Does One Get The Dagger; "sawtooth"

I saw this legendary dagger in the item guide:

• Slots: 2
• Restrictions: Untradable
• Damage: 50-100
• ✹ Fire Damage: 10-20
• ❉ Water Damage: 10-20
• ❋ Air Damage: 10-20
• ✦ Thunder Damage: 10-20
• ✤ Earth Damage: 10-20
• Attack Speed: Super Fast

• Lv. Min : 91
• Strength Min: 20
• Dexterity Min: 20
• Intelligence Min: 20
• Agility Min: 20
• Defense Min: 20

• Spell Damage: +15%
• Melee Damage: +15%
• ✹ Fire Damage: +15%
• ❉ Water Damage: +15%
• ❋ Air Damage: +15%
• ✦ Thunder Damage: +15%
• ✤ Earth Damage: +15%

It's called Sawtooth... It's really OP but it's untradable... How do ya get it?
If you know... please tell me... This reallys seems great for my melee/damage but :)

Thank you, -Reefive (that is corrupted by Bill Cipher...)

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Oh wait... I should of put this in Questions... DAMN

 

Fallen Factory I think

 

Ok... Thanks... I'll try later ;)