Excalibur, Sword of Eden All that talk about swords being power crept, and WotC was like, okay, hold my beverage
Big Mother Mouser | 4 Colorless Mana Artifact Creature Robot This creature enters with two +1/+1 counters on it
Narset, Parter of Veils works perfectly
It's a rare mana ramp card in Esper colors that even includes milling
Not only does it protect our board against wipes by making it so that we Amass whenever a Sliver dies, but it also gives Slivers we control Afflict 2 which disincentivizes our opponents from blocking
Furthermore, there are many more widely played formats (such as Tiny Leaders) I could provide a link to, but the reality is that if you include all those formats in your definition of previously banned, some person will eventually just invent a format that bans every card but basic lands, and therefore will be able to tutor all cards