(Artifacts, legendaries, and sagas are historic.) A card, spell, or permanent is historic if it has the legendary supertype, the artifact card type, or the Saga subtype
Even if the opponent chooses to trade blows, the weakening effect lasts until the start of your next turn, so it won't go to waste
If a creature you control being dealt damage causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time
But, if we discount that as merely a mini add-on to the 291-card March of the Machine, the smallest legitimate set is Arabian Nights , the very first 'expansion' set, released in December 1993 with just 92 cards
3: Emeritus Of Ideation I do not think I could do a top 10 without including [[Emeritus Of Ideation]]
Four additional borderless cards can be found in the Outlaws of Thunder Junction Commander set (OTC)