I was thinking lately about this item. We all know that it is not the best out there and if may I say, it is mostly useless since many items do its job a lot better.
Since my beggining in LOL about 2 and a half years ago I remmembered this item and it was even worse back then. I feel that this item is in the same spot in which Hexdrinker used to be. An item with nice effect and many uses but overall, too weak stats, unexpanded possibilites and unachieved power.
So I want to suggest something like this.
+30 attack damage (5 damage buff, I think its reasonable).
+20% critical strike (it is nice as it is)
Unique: Your basic attacks inflict Grievous Wounds on enemy champion for 2 seconds, 1.5 for ranged seconds. (I inserted longer time for mele because mele need to get in range to attack while ranged can constantly attack you while being far away).
Executioner's Calling + Bilgewater Cutlass = Viper
1900 + 1400 = 3300 + 550 recipe = 3850
+65 attack damage
+25% critical strike
+100 (maybe a little bit less, just testing) attack range (ranged only)
Unique: Your basic attacks inflict Grievous Wounds on enemy champion for 2 seconds, 1.5 for ranged seconds. (AD stealing part is deleted because with new aditions it does too much).
Active: Fires a twin fang from Viper which slows for 30% for 2.5 seconds and deals 200 magic damage. In addition, it stops health regen and any spellvamp and lifesteal effect for 4 seconds, cooldown 90 seconds. Healing from other sources (eg Soraka's ultimate) won't be affected by this. (I capped it to two seconds because if I give it more, Mundo would become unplayable, and not just Mundo but every other champion that relies on a skill that gives massive regeneration, might drop this active in favor of something else).
Numbers might be a little bit wacky but the concept is an item that performs nice, has nice stats and can help you greatly in moments when someone who benefits from self healing like Akali or Warwick attacks you. Many times I've seen Fiora going with blood thirster and Hydra and no one could stop her because she was regenerating too much even with Grievous wounds debuff.
Also, what would you like to see in Viper's stats? Tell me what you think about it. I know one thing for sure, that sword needs Hexdrinker therapy STAT!
EDIT1: Updated new stats according to your feedback.
EDIT2: Added a new passive that will make some carries really happy.
EDIT3: Cooldown on active reduced to 90 seconds, active duration increased to 4 seconds, price retuned to 3850 gold.