Poison the Waters ought to be an excellent sideboard card, and its probably good enough to make the main deck in more controlling black decks
While other Rings of Power were forged for Elven-kings, Dwarf-lords, and the Mortal Men of Middle-earth, there is only one that matters most: the One Ring to rule them all
You'll drop their cost by their power
Depending on their budget and available space, Players can usually benefit from organizing their collection by Ink Colour instead of by Set
I've had a ton of games with Bogles where you flood out and are stuck just sitting on a ton of excess mana with no way to utilize it
This blue instant also counters artifacts, Karn, etc., and also fizzles lots of stuff while replicating into Ashling triggers, which allows an Izzet deck to be pesky while converting into while rummaging/drawing three cards and dishing out a one-sided Pyroclasm