You have ten seconds to search your library and reveal a card with the chosen item in its art
While Counterspell is the most well-known, Id recommend Arcane Denial as the must-include counter
You may choose Rat creature cards milled with this ability
You can really tear up a hand in Premodern if youre on the play with black by, say, turn one Dark Ritual into Cabal Therapy, then playing a two-drop creature, say, Ravenous Rats (making them discard a card), and then flashback Cabal and sac Rats, then Unmask paying the alt cost of discarding a black card
Doctor Who arrives in the Commander format with four preconstructed decks
Cards like Underworld Dreams and Sheoldred, the Apocalypse are great picks here, as are Waste Not and Megrim