Haste, as a keyword, came first (five and a half years earlier).

Both abilities appeared on a card in Alpha (on Nether Shadow and Serra Angel, respectively), but neither started as a named keyword. Haste would show up first in Sixth Edition as part of the Sixth Edition rules change in April of 1999. Up until that point, R&D had nicknamed it "celerity," named after a similar ability, flavor-wise, in the Vampire: The Eternal Struggle Trading Card Game. Vigilance wouldn't show up as a named keyword until Champions of Kamigawa in October of 2004. We talked about keywording both effects for many years before we finally did it.

The legendary supertype came first (nine years earlier).

The legendary supertype first showed up in the expansion Legends in June of 1994 which introduced the concept. Interestingly, on creatures, it was originally a creature type (Legend), but the set also introduced lands that had legendary as a supertype. While basic lands first showed up in Alpha, basic as a supertype didn't show up until Eighth Edition in July of 2003.

The creature type Mutant came first (one year earlier).

While the word Mutant first appeared in a card title in Ice Age on Goblin Mutant back in 1995, it didn't show up printed on a card until Mistform Mutant in Onslaught in October of 2002. Humans, creatively, had been part of Magic from the very beginning but didn't show up as a creature type until Mirrodin in October of 2003 where it was part of the introduction of the race/class model for creature types where creatures could get creature types representing both what they are as well as what they did. Prior to that, Humans just listed what they did as their creature type. The addition of Humans as a creature type was controversial at the time but has since gone on to be a normal part of the game. R&D specifically avoided making them matter tribally until original Innistrad.

The keyword exile came first (two years earlier).

The keyword exile was introduced in the core set Magic 2010 in July of 2009. The concept had existed since Alpha (Swords to Plowshares probably being the most memorable) but was called "remove from game." The term confused players as it wasn't really removed from the game being there were effects that could interact with the card, so the Magic 2010 rules change created a new term for it. The keyword fight was first introduced in the original Innistrad in September of 2011. R&D had experimented with various ways to force two creatures to rumble with one another, but usually it was done by manipulating combat. The fight keyword allowed the two creatures to do it at any time and proved to be an important tool to give green needed creature control that was in color pie (as it required a big enough creature to work properly).

Four loyalty abilities came first (a year and a half to nine years earlier).

The first planeswalker with four abilities was Jace, the Mind Sculptor from Worldwake in February of 2010. The first planeswalker with a static ability was technically Garruk Relentless in Innistrad, but static abilities as a regular thing didn't appear up until War of the Spark in May of 2019 where it was a feature of all 36 planeswalkers in the main set. Interestingly, when we first designed planeswalkers, we came up with both planeswalker advancements but held off on each of them until we felt the time was right. The reason static abilities took longer was because we knew they were opening up a whole lot of design space and we wanted to make sure we'd explored the existing space first. Once they were available, we knew it would be hard going back.

Noncreature enchantment tokens came first (three years earlier).

The first enchantment token, noncreature or not, was created by Imperial Mask in Future Sight in May of 2007, and it made token copies of itself. It was a "futureshifted" card so it was hinting at things we might do in the future. The first card capable of making a noncreature artifact token was Prototype Portal from Scars of Mirrodin in October of 2010. It could copy any artifact, so often the token would be an artifact creature token, but it could copy a noncreature artifact. The first set to introduce artifact tokens as a larger feature was Shadows over Innistrad in April of 2016, which introduced Clue artifact tokens.

Off-color activations came first (ten months earlier).

The first off-color activation was in Alpha in August of 1993 on Sedge Troll, a red card with a black activation. Multicolor cards would show up for the first time in Legends in June of 1994.

Collector numbers came first (eight months earlier).

Collector numbers appeared for the first time in Exodus in June of 1998. They appeared for the first time along with color indicators to tell rarity (black for common, silver for uncommon, and gold for rare—mythic rare wasn't a thing yet). Foil, or premium cards as we initially referred to them, first showed up in Urza's Legacy in February of 1999. Interestingly, both innovations were the result of the same Magic brand team who were trying to apply elements found on other trading cards to Magic cards.

Planeswalkers came first (one year earlier).

The first set with planeswalkers was Lorwyn in October of 2007. The original plan had been for them to premier as three "futureshifted" cards in Future Sight, the previous set, but R&D pushed the new card type back to give us more time to work on their design. The first set with mythic rare cards was Shards of Alara in October of 2008.

Substitute/checklist cards came first (five and a half years earlier).

The checklist cards first appeared in original Innistrad in September of 2011 to indicate what double-faced cards were in your deck if you weren't playing with opaque card sleeves. The original plan was to make double-faced cards one sided and have them fetch the double-faced version when cast, but the printers at the time couldn't guarantee the two cards showing up together in boosters, so we had to find another solution. The keyword counter punch-out cards first appeared in Amonkhet in April of 2017. They had tokens you could punch out to indicate -1/-1 counters, brick counters, or something being embalmed or exerted.

A set with a major graveyard theme came first (a year earlier).

The first set with a major graveyard theme was Weatherlight in June of 1997. The first set with a major enchantment theme was Urza's Saga in October of 1998. The block was referred to as "The Artifact Cycle" for story reasons and had several overpowered artifacts in it, so its enchantment theme often gets overlooked. Theros in September of 2013 is the first set with an enchantment theme that didn't get overshadowed by other themes.

Alternate art came first (four years earlier).

The first set to have alternate art for the same card was Antiquities in March of 1994. All the lands, save Mishra's Workshop, had alternate versions of their art, although not all at the same occurrence. This was done to add a little variety to the lands, which showed up in a lot of packs (Antiquities only had 85 cards in it). The first full-art lands appeared in Unglued in August of 1998. Full-art lands had been pitched by artist Chris Rush years earlier, but no one else thought the players would be interested. I loved the idea, so I put them in my "weird" set, and no one said anything about it. The lands would go on to be hugely popular, eventually showing up in a premier set in original Zendikar in October of 2009.

Cards referencing an unprinted card came first (sixteen months earlier).

The first card to reference the name of a card not yet printed was Shield of Kaldra from Darksteel in February of 2004. It was part of three artifacts connected to Kaldra that had an effect if you got all three onto the battlefield together. We had done broader hints about future products before, but this was the first time we gave an actual name of an upcoming card. The first card without a mana cost was the card Evermind from Saviors of Kamigawa in June of 2005. The card had splice onto arcane, which allowed you to play it even though you could never cast it.

Four-color cards came first (five and half years earlier).

Transform

The Nephilim cycle in Guildpact in February of 2006 had the first four-color cards in the game. We designed them because we were asked to make a cycle for players who might not like the guilds theme. Four-color cards had been a frequent request, and Guildpact was a multicolor set. The color indicator was introduced in the original Innistrad in September of 2011 to define the back sides of double-faced cards without having to resort to characteristic-defining abilities.

An artifact with color in its mana cost came first (three years earlier).

The first artifact with color in its mana cost was the futureshifted card Sarcomite Myr in Future Sight in May of 2007. The first enchantment with no colored mana was Eldrazi Conscription in Rise of the Eldrazi in April of 2010.

Defender as a keyword came first (a year and a half earlier).

The first set to use defender as a keyword was Betrayers of Kamigawa in February of 2005. The first set to use flash as a keyword was Time Spiral in October of 2006. Both abilities predated their keywording by many years. Defender, as an ability, first showed up in Alpha and was baked into the Wall creature type. Flash, as an ability, first showed up in Mirage on a cycle of creature Auras.

The colorless mana symbol in mana costs came first (three and a half years earlier).

The colorless mana symbol first appeared, both in a mana cost and in the rules text, in Oath of the Gatewatch in January of 2016. The concept of colorless mana goes all the way back to Alpha, but it used the same symbol as generic mana. When Oath of the Gatewatch started using it in mana costs, it forced us to create a separate symbol for it, which is now evergreen. The first set to use snow mana in mana costs was the first Modern Horizons in June of 2019. Snow mana was first created in Coldsnap in July of 2006, but it was only used in activation costs and not mana costs.

The term "enters the battlefield" came first (two years earlier).

"Enters the battlefield" was introduced to the game with the Magic 2010 rules change in July of 2009. It replaced the term "comes into play," which first appeared in the set Portal in June of 1997. "Dies" was first introduced to the game in Magic 2012 in July of 2011.

The mana value 10 or higher came first (six months earlier).

The first card with a mana value 10 or higher was Aladdin's Lamp from Arabian Nights in December of 1993. At the time, they didn't know how to fit a ten in a colorless mana symbol, so the card lists two fives instead of a single ten. XX first appeared in a mana cost on two cards, Part Water and Recall, in Legends in June of 1994.