Thought Ruler Archfiend's effect is when it destroys an opponent monster by battle and sent it to the grave, you gain life points equal to the destroyed monster's attack.
Armory Arm's effect is the equip monster equip with this card gains 1000 attack and if it destroys an opponent monster by battle and sent it to the grave, inflict battle damage to your opponent equal to hte destroyed monster's attack.
So, if you equip Armory Arm to Thought Ruler Archfiend, it will gain 1000 attack. And everytime when it destroys an opponent monster by battle and sent it to the grave, you inflict battle damage to your opponent equal to the destroyed monster's attack and you gain life points equals to the destroyed monster's attack!
Armory Arm's effect is the equip monster equip with this card gains 1000 attack and if it destroys an opponent monster by battle and sent it to the grave, inflict battle damage to your opponent equal to hte destroyed monster's attack.
So, if you equip Armory Arm to Thought Ruler Archfiend, it will gain 1000 attack. And everytime when it destroys an opponent monster by battle and sent it to the grave, you inflict battle damage to your opponent equal to the destroyed monster's attack and you gain life points equals to the destroyed monster's attack!
Psss : Please check out poll 2 :)