Annul is strong against Landstill's Standstill, and it also counters Humility and the artifact lock/utility pieces like Powder Keg and Phyrexian Furnace as they are cast. It can't touch their counterspells, Swords to Plowshares, or Wrath of God, so it is purely a answer to their permanents. Overload is a narrow, cheap answer to Powder Keg (mana value 2) or Phyrexian Furnace, and it can also destroy an animated Mishra's Factory (mana value 0). Note that Powder Keg only destroys artifacts and creatures with mana value equal to its fuse counters, so it cannot hit Stasis itself. Thwart comes out because Landstill's own Counterspell and Mana Leak density makes tempo-countering less reliable than preventing their lock pieces from resolving in the first place. Black Vise comes out because it is a slow clock that is vulnerable to Disenchant and Powder Keg and can be countered, so it is the weakest card to give up for the answers above.