you with this weapon Crit on an attack roll  with a 19 or 20 

When you roll a 20 on your attack roll with this magic weapon, the target takes an extra 2d6+10 damage of the weapon’s type.

Proficiency with a Battleaxe allows you to When you roll a Crit  on your attack roll with this magic weapon, the target takes an extra 1d6+(Proficiency bonus) Necrotic damage.

When you Roll a Crit on your attack roll with this magic weapon, Get Temp HP equal to damage dealt 

when you kill/slay with this weapon, you Recover one forth (1/4) of Bleed-Over Damage Rounded down as health + CON  Mod. If there's not any Bleed-Over damage or Bleed-Over damage is  equal to zero after rounding down the CON Mod is not added and this effect will not take place.If the target killed is a Construct this effect will not take place.If the target killed is Undead  Then half the amount of Heath (HP) recovered after adding the CON mod . 

When you kill on a Crit you can chose one non-magical ability recover one charge/use/point of the ability chosen. (rage, Ki,etc)

When Attuned it has +2 to attack and damage rolls When un-Attuned it Only Has +1 to attack and damage rolls. (note this is the only ability That will be active Before the Attunment-Challenge has Bin-met .)

When Attuned all Buffs applied to you or an object on your person Have there duration extended by a number of minuets equal to your character level.

 When in battle you Have advantage on saving throws against the application or removal of  non-instantaneous Debuffs (Negative effects that don't resolve at instantaneous speed and have a prolonged effect.)

 when in combat You are unaffected By Exhaustion you remain unaffected for the Next 1 hour after (.note Exhaustion is not removed by this effect)  

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

Notes: Damage: Additional, Immunity: Exhaustion, Damage: Necrotic, By Devouring The enemy's Blood and Suffering the Warrior can fight for an eternity, Slaying 100 enemy's in one battle with out rest or Slaying 1000 enemy's with this weapon which ever happens first , Healing, Damage, Buff, Combat, Sentient, Versatile, Topple