Shadowmoor is a Magic: The Gathering block consisting of the expansion sets Shadowmoor (May 2, 2008) and Eventide (July 25, 2008). It was originally planned as part of the Lorwyn block, but partway into the design of Lorwyn, that block was changed to a two-set block and Shadowmoor was released as the first set of a second two-set block. The two blocks were linked through synergy and rotated through the official tournament formats as a single, four-expansion unit.
Shadowmoor is the first set of the Shadowmoor block, which started May 2008. Shadowmoor is the first large expansion to be released in a month other than October since Ice Age’s June 1995 release. The designers of the set are Mark Rosewater (lead), Sean Fletcher, Mark Gottlieb, Devin Low, and Ken Troop; the developers of the set are Aaron Forsythe (lead), Devin Low, Alexis Janson (the winner of The Great Designer Search Contest), Matt Place, Jake Theis, Steve Warner, and Doug Beyer. The Shadowmoor symbol might suggest a bat wing or dead leaf, but is a Jack-o'-lantern lid taken from the art of the card Reaper King, the King of the scarecrows, a prominent creature type in the set. The set's theme is color, utilizing hybrid (introduced and last seen in the Ravnica block) across the allied color pairs, along with innovations in hybrid mana. A new action is introduced in this set, called "Q", representing the untap symbol; according to Rosewater, this has "never [been] done before." Rosewater also stated that "the set plays into the duality theme between Lorwyn and Shadowmoor blocks, both in the art and the mechanics." For example, the same creature types from Lorwyn returned.
The set plays on the same plane as Lorwyn, but due to an event called the Aurora, the plane and its inhabitants are twisted and changed. The art of Shadowmoor's booster packs depicts familiar Lorwyn creatures either during or after a dark change. As such, there are a number of mirrors between the Lorwyn and Shadowmoor blocks (For example, Lorwyn focuses on tapping and +1/+1 counters, while Shadowmoor focuses on untapping and -1/-1 counters)
More than 25 cycles have been identified in this set, including a number of "mega-cycles" that include five allied-colored cards from Shadowmoor and five enemy-colored cards from Eventide. Rosewater has noted that the set is a "little cycle heavy".
Five theme decks were released as part of the set. The preconstructed theme decks are: "Aura Mastery" (White/Blue), "Mortal Coil" (Blue/Black), "Army of Entropy" (Black/Red), "Overkill" (Red/Green), and "Turnabout" (White/Green).
Shadowmoor introduced the mechanics conspire, persist, untap and wither.
Conspire - When you play a spell with conspire, you may tap two creatures that share a color with it to copy the spell, choosing new targets if desired.
Persist - When a creature with persist is put into a graveyard from play, if it had no -1/-1 counters on it, it returns to play under its owner's control with a -1/-1 counter on it.
Untap - The untap keyword action now has a symbolic representation which only appears in costs of activated abilities.
Wither - A creature with wither deals damage to creatures in the form of -1/-1 counters.
Shadowmoor also introduced the monocolor hybrid mana symbol, a hybrid symbols displaying a number and a color mana symbol can be paid for with either the number of colorless mana depicted or the colored mana. The converted mana cost of these cards is the highest possible cost that they can be paid for with. Examples of this are shown in a cycle including cards such as Tower Above and Beseech the Queen. Reaper King also has a monocolor hybrid mana in its manacost, but it has one monocolor hybrid mana symbol for each color, making it the only multicolored card with all of the monocolor hybrid symbols.
Five theme decks were released as part of Eventide. The preconstructed theme decks are: "Life Drain" (White/Black), "Sidestep" (Blue/Red), "Death March" (Black/Green), "Battle Blitz" (Red/White), and "Superabundance" (Green/Blue). The Eventide booster packs also include a rules card/token card in addition to the normal 15 game cards.
Eventide continues the block theme of hybrid cards and color matters that Shadowmoor started, as well as further use of the Wither and Persist key words. Where Shadowmoor focused on allied color hybrids, Eventide focuses on enemy color hybrid cards. Eventide also introduces two new mechanics: