Basalt Monolith and Grim Monolith come to mind
This adds an extra step to progression, as you are not just playing a card but also building the space it will go into
And I'd rather get it destroyed occasionally before drawing a card since usually you'd draw many
Ill be upfront with you, I hated Secret Lair x The Walking Dead the second it was announced
Sin, Spira's Punishment Squall, SeeD Mercenary These Through the Ages cards are also worth splashing: Winota, Joiner of Forces Bruse Tarl, Boorish Herder Kenrith, the Returned King Kraum, Ludevic's Opus Muldrotha, the Gravetide Mythics As with rares, the mythics youll want to splash are basically just bombs
Really, Sister of Silence wouldve been fine without the ability to counter instants and sorceries as well, thats just an extra bit of protection against those board wipes