20 cards where the card is tagged “opponent-discard-matters”

Abyssal Nocturnus (Guildpact #43)
Dream Salvage (Shadowmoor #160)
Duskmantle Guildmage (Gatecrash #158)
Fell Specter (Jumpstart #233)
Geth's Grimoire (Darksteel #123)
Lazav, Dimir Mastermind (Zendikar Rising Commander #92)
Liliana's Caress (Magic 2011 #103)
Megrim (Magic 2010 #104)
Nath of the Gilt-Leaf (Commander 2016 #213)
Nihilith (Commander Legends: Battle for Baldur's Gate #765)
Quest for the Nihil Stone (Worldwake #64)
Raiders' Wake (Ixalan #116)
Sangromancer (Commander 2021 #152)
Syr Konrad, the Grim (Murders at Karlov Manor Commander #141)
Tergrid, God of Fright // Tergrid's Lantern (Kaldheim #112)
Tergrid, God of Fright // Tergrid's Lantern (Kaldheim #112)
The Haunt of Hightower (Ravnica Allegiance #273)
Tinybones, Trinket Thief (Jumpstart #17)
Tourach, Dread Cantor (Modern Horizons 2 #102)
Vulturous Zombie (Commander Anthology Volume II #170)
Waste Not (Commander 2016 #117)

The message was clear to Sorin—time to search for something else.