The Dark/Trivia

Main article: The Dark

Ashes to Ashes and Dust to Dust not only have related names, they also have similar costs and effects.

Trivia by color

Merfolk Assassin combos with War Barge, which is also printed in this expansion, to kill any creature for ,.
Water Wurm is the only blue wurm.

Frankenstein's Monster is one of only a few cards named after a literary source. It is also the only card that stipulates three different types of counters that can be put on it, something that is avoided today.
Murk Dwellers likely inspired the creation of cards that gain a power bonus when attacking, such as Charging Bandits, Hollow Dogs, and Ravenous Skirge.
Nameless Race is the only non-artifact creature without a creature type.
Rag Man is mentioned in the flavor text of Dauthi Trapper.

Goblin Rock Sled created confusion for having "Goblin" in its name but not in its creature type, making it unclear to many at the time how it interacted with other cards in The Dark that referenced Goblins.
Inferno inspired the creation of Bloodfire Colossus.
Mana Clash is the only card with a casting cost of that can potentially win the game on the first turn without any other assistance. This card is named after one of a few names considered for a time for the title of the game of Magic, which was considered too common a word to trademark; ": the Gathering" was later added to "Magic" to make it unique.

Gaea's Touch was initially misprinted with all its text, expansion symbol, and mana cost shifted to the left.
Marsh Viper is the only creature in this expansion with the Poison mechanic.
Venom gave the ability of Thicket Basilisk, Cockatrice and Infernal Medusa a name to be referred by.
Whippoorwill, along with Frozen Shade and Blinking Spirit, confused many players by depicting a creature apparently in mid-flight in its art without actually having flying. This kind of disparity between art and ability is actively avoided in modern cards. ^[1]

City of Shadows inspired the creation of Altar of Shadows.
Coal Golem has an ability that allows any deck to cast Ball Lightning. It inspired the creation of the Attendant cycle in the Invasion expansion, each of which has a similar ability that allows any deck to cast one of the corresponding Legendary Dragons from the Legendary Dragon cycle in the same set.
Maze of Ith was restricted in the Vintage format from October 1994 until April 1999 for its ability to slow games significantly. This card was heavily played due to its power, and under old Mulligan rules resulted in many opening hands without mana sources.
Reflecting Mirror is the first card to have the ability to change the target of another spell.
Safe Haven has an ability that originally functioned at interrupt speed because there were a few cards (such as Red Elemental Blast) at the time that could kill a creature at interrupt speed. It inspired the creation of Cold Storage.
Sorrow's Path is voted to be "the worst card (in terms of power) ever made" by Mark Rosewater.
Stone Calendar inspired the creation of the Medallion cycle in the Tempest expansion, which further inspired the Familiar cycle in the Planeshift expansion and the Warchief cycle in the Scourge expansion.

Dark Heart of the Wood is the first multicolored non-creature card, and the first enemy color pair card. Cards for the other four enemy color pairs were not printed until Mirage.
Marsh Goblins and Scarwood Goblins are the first non-Legendary multicolored creatures.

Sorted by decreasing combined power and toughness.

Leviathan (10/10) had the greatest combined power and toughness among all creatures until Polar Kraken in the Ice Age expansion; it is also the first creature printed with double-digit power and toughness.
Carnivorous Plant (4/5) has the greatest combined power and toughness among green creatures in The Dark. It was the first Wall without "Wall" in its name, leading many players to think that it could attack.
Diabolic Machine (4/4) has the greatest combined power and toughness among artifact creatures in The Dark.
Eater of the Dead (3/4) has the greatest combined power and toughness among black creatures in The Dark.
Ball Lightning (6/1) has the greatest combined power and toughness among red creatures in The Dark. It inspired many hasty disposable creatures, including Skizzik, Blistering Firecat, Spark Elemental and Lightning Serpent. Before receiving errata, Ball Lightning only had to be sacrificed "at the end of the turn during which it was summoned" instead of at the end of any turn, allowing some loopholes around its intended impermanence before errata was issued to fix it. This artwork can also be found in the artwork of Dwarven Shrine.
Knights of Thorn (2/2) has the greatest combined power and toughness among white creatures in The Dark.