Ability word: Also known as a pseudo. An italicized keyword ability. On cards, it is followed by a long dash and rules text written out in full. Ability words have no inherent rules meaning, instead serving as markers to indicate common themes. Imprint was the first mechanic to be formatted as an ability word, though the older mechanic threshold has since been errataed into one. Other examples include bloodrush, domain, and revolt.

Action keyword: A keyword ability formatted as an instruction. Regenerate was the first mechanic to be formatted as an action keyword, but scry was the first non-evergreen example (as regeneration was evergreen at the time). Other examples include proliferate, detain, and investigate.

Arcun: Short for "archetype uncommon". A multicolored (usually two-colored) uncommon card designed to signal and support a specific deck archetype in Limited.

Bend: A color pie divergence slight enough and infrequent enough to be justified by set themes or flavor.

Break: A color pie divergence too significant to be justified by set themes or flavor. A blue card with double strike or a black card that destroyed artifacts or enchantments, for example, would be a break. Many, many words have been spent on the distinctions between bends and breaks.

Clever: While it's often used to praise cards that are actually clever, this word has also become something of a backhanded compliment for cards that seem to value quirkiness or unusual rules interactions above playability. The classic example is the one-mana sorcery-speed counterspell - creates a nice "aha!" moment, but often a completely dead card in practice if you're caught without a Quicken effect. "Cute" has a similar meaning.

Color density: The number of colored mana symbols in a card's cost. Higher color densities allow for more powerful cards, especially at low costs, because they make a spell harder to cast efficiently. Cancel, for example, has a color density of 2.

Color pie: The division of abilities and effects among the five colors of Magic. Recently codified by Mark Rosewater in his Mechanical Color Pie article, which divides various abilities and effects into primary, secondary, and tertiary categories for each color.

Deciduous: A category of mechanics one step down from evergreen. Deciduous mechanics are not expected to appear every set, but can appear with no special justification if they contribute to the set's themes. Hybrid mana, double-faced cards, Curses, and Vehicles are all considered deciduous by WotC; some custom designers add their own candidates, with cycling being a fairly common example.

Deeptapping: Also known as freezing. Tapping a permanent and preventing it from untapping during its controller's next untap step.

Dies to removal: An oft-cited and oft-derided retort to claims that a creature is too powerful. Generally, "dies to removal" should be considered the default rather than a drawback, and not dying to removal, thanks to an ability like hexproof or a toughness higher than most of the environment's viable burn spells, should instead be considered an upside. Especially egregious when applied to noncreature cards, which some colors flat-out can't remove.

Downside mechanic: Also known as a drawback mechanic. A keyword ability that's pure downside unless you have a particular way to profit from it. Largely out of favor nowadays, because keywords are supposed to be exciting to players and downside mechanics tend to do the opposite even when printed on otherwise overpowered cards. Echo, vanishing, and cumulative upkeep are all downside mechanics.

Evergreen: A keyword ability codified as a constant part of Magic which can appear in any set, often without reminder text. The current suite of evergreen mechanics includes deathtouch, defender, double strike, enchant, equip, fight, first strike, flash, flying, haste, hexproof, indestructible, lifelink, menace, prowess, reach, scry, trample, and vigilance.

Impulse draw: Exiling cards from the top of your library which may be played this turn only. A mostly red effect, named for the card Act on Impulse.

Keyword soup: Refers to several different keyword abilities, usually at least four, appearing on a single card. Works for the occasional rare or mythic, but often hard to keep track of and something of a brute-force approach to making powerful cards.

Kill your darlings: Design aphorism, originally from the film industry. Loosely translated, if you come up with a card or mechanic that you're absolutely certain is the best thing you've ever created, it should probably be scrapped lest your attachment to it blind you to its issues.

MSE Modern: Formally known as MSE Modern 2.0, often abbreviated to MSEM. A custom Constructed format, played through LackeyCCG, featuring a curated selection of the MSE forum's best sets. Aims for a power level roughly on par with Modern, hence the name.

New regeneration: Gaining or granting indestructible until end of turn, an ability now used instead of the retired regenerate keyword.

Omniverse: An MSE forum term for the five extra colors added by the "Magic New Extra" template and its sequels: brown (E), pink (K), purple (P), yellow (L), and orange (O), sometimes abbreviated to EKPLO. Various efforts have been made to establish the identities of these colors either as an alternative to or in addition to the five canonical Magic colors.

Parasitic: A card or mechanic that relies heavily on something only available in its own set. Parasitism is not always bad on individual cards, but parasitic mechanics are problematic because they limit how far they can be combined with cards from other sets. The splice onto Arcane keyword from Kamigawa block is a good example of a parasitic mechanic.

Primary: A color's primary effects are things it always has unconditional access to.

Redflag: A tool used by some designers to limit the complexity of a set, especially at common. New World order recommends that any common card which breaks certain soft rules should be redflagged, such cards should need a good justification to break those rules, and no more than 20% of your commons should be redflagged. A somewhat outdated primer by Reuben Covington may be found here.

Secondary: A color's secondary effects are things it has access to, but not as frequently as primary effects and often with some caveats, such as rarity restrictions or restrictions to specific kinds of card.

Smalltext: A card with very small text, making it hard to read (remember that MSE renders are almost twice the width and height of actual Magic cards). Usually caused by either excessively complex rules text or flavor text on a card without room for it. Anything more than eight lines of text is generally agreed to be smalltext.

Smoothing: A mechanic that helps you avoid situations where there's nothing relevant you can do by improving the quality of your draws or the cards in your hand (sometimes also applied to mana production). Generally good, but excessive smoothing can make decks too consistent. Scry and cycling are examples of smoothing mechanics.

Strictly better: One card is strictly better than another if the only mechanical differences the former has from the latter are upsides - costing less, hitting more targets, having better stats or extra abilities, and so on. Creature types are usually not counted, as they're too situational.

Strictly better than a basic: A common response to some nonbasic land designs, referring to the R&D rule that no land is allowed to be strictly better than a basic land, i.e. always better or more flexible in a vacuum. If a land makes more than one color of mana with no downside, or it makes mana of a single color with no downside and has additional abilities, it's strictly better than a basic. Things that don't exempt lands from this criticism: the four-copy limit (still no reason not to replace four basics with them), being nonbasic (only relevant against some land destruction), lacking basic land types (only relevant in formats with fetches and a few other effects), having other types that make them vulnerable to more types of removal (see dies to removal). The jury's out on whether being legendary is enough of a drawback on its own.

Square: A creature with equal power and toughness - "square stats".

Swingy: A card or ability that varies a lot in effectiveness depending on the game state. Usually used in a negative light to refer to cards that are either completely useless or absurdly powerful.

Tertiary: A color's tertiary effects are things it can access only occasionally, and often with heavy restrictions. Some aspects of a color's tertiary portfolio may be considered bends when used, depending on the exact circumstances.

Threshold mechanic: A mechanic, usually an ability word, that acts like a switch that "turns on" when a certain condition is met. Named after threshold, the first mechanic of its kind; other examples include metalcraft and ferocious.

Win-more: An effect that's at its most powerful or useful when you're already doing well. Generally advised against unless you have a very good reason for it.