It's unclear whether this was the most necessary of the Slivers, but it was the one that frustrated the most opposing plans to deal with the problem and even opened up new game plans when the card advantage resulting from saving your creatures could allow Sliver decks to go the control route when backed up by counters and removal spells
It shuts down other effects as well - your opponents can't cast spells from anywhere other than their hands, so no casting spells using Madness, Plot, Mayhem, or a whole bunch of red impulse draw effects
It's super cheap but it cannot stop tramplers, and it's on the ground
Facilier: Agent Provocateur is a powerful card against standard starter deck compositions, allowing characters banished in a challenge to be returned to the hand thanks to the Into the Shadows ability
Since August 2024, Wizards of the Coast has said MTG banlists should happen once a year, except in rare, particularly urgent circumstances