Executioners calling is an 800 Gold item that gives 15 AD and the Passive "Executioner" which after dealing Physical damage to an enemy champion applies Grievous Wounds to that opponent for 3 seconds. Although 15 AD for 800 Gold is not that good, having Grievous Wounds on your team can make or break a game. The flip side of this for AP champions is a 3000 Gold investment, Morellonomicon. This Item provides 70 AP, 300 HP, 15 Magic Pen, and the passive "Cursed Strike" Magic Damage inflicted on an opponent causes Grievous Wounds for 3 seconds. The cost of obtaining Grievous Wounds on an AD champion is way too low compared to the cost on the AP side. My suggestion for this is to change Executioners Calling to build like Caufield's and Serrated Dirk, 2 longsword build path and a total cost of 1100g. The item would give 25 AD and Grievous Wounds. Then make a new AP item that costs approximately the same (depending on balancing) and builds like Hextech Revolver, 2 AP tomes. That new item plus Oblivion Orb would build into Morellos. This would create a much more balanced level of gameplay against self healing champions. Grievous Wounds items should not be extremely gold efficient. They should be a significant investment to counter specific types of champions but it should be equal on the AD and AP side. It seems very odd and outdated to have such a large gold discrepancy just to get the same passives.
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TL;DR Grievous Wounds is only 800g away for an AD champion vs the 3000g for an AP champion. This is unbalanced gameplay and a lower costing AP item should be introduced to balance this.