Let Counterbalance resolve, revealing Armaggon to counter their Darksteel Monolith
The other cards are sweet, but I particularly like that The Spear of Leonidas has three choices when you attack with it, including summoning Phobos, a legendary 3/2 red Horse creature token
Its a little more niche, but it triggers much more often than you think
The rad counters can trigger the milling, but youre obviously going to want to include a lot of other ways to mill in your deck
Bitter Ordeal Cranial Extraction Denying Wind Dichotomancy Dimir Machinations Extract Haunting Echoes Jester's Cap Kotose, the Silent Spider Lobotomy Lost Legacy Memoricide Neverending Torment Nightmare Incursion Pick the Brain Reap Intellect Sadistic Sacrament Stain the Mind Supreme Inquisitor Thought Hemorrhage Titania's Command
It was allowed to ravage Commander games for far too long, eventually earning itself a spot on the banlist due to the sheer amount of Treasure this could pump out in 4-player games