New and Updated Rules For detailed descriptions of each of the new mechanics, check out Matt Tabak's excellent mechanics article
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
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Originally in the sideboard and in the deck while Jadelight Ranger was, but without more sources of green mana, casting Shapers Sanctuary early is quite difficult, and the card is at its best when it comes down before any creatures enter the battlefield
Preposterous Proportions Marcy: This is like the epitome of 'big dumb green' and frankly I love it
Four power at instant speed for three mana is often what you want, and the enchantment option being castable at instant speed makes it quite the nightmare for opponents