Unblockable

Unblockable is a slang term used to describe the mechanic that prevents creatures from being blocked.

On cards it appears as can't be blocked.

Activation
This ability must be present prior to the blocking phase for it to work.

For cards like Frilled Sea Serpent who need to spend mana to activate this ability temporarily, it needs to be activated prior to the actual blocking phase, during the attacking phase.

Activating it after a blocker has already been assigned does not negate that block: the card must be enhanced prior to the blocking declaration.

History
R&D tried to keyword this evasion ability only to discover that there are so many variations on it that they couldn't. Officially, it used to be an attribute of a creature, until it was made obsolete in Magic 2014 when the text Is unblockable was changed to Can't be blocked to make it very clear that "unblockable" is not an ability. Cards that used the term have received errata in the Oracle card reference. Can't be blocked is primary in blue, which has both creatures with this ability and grants it through spells and Auras.

Granting unblockability
A creature's ability that grants unblockability can be static (Covert Operative), triggered (Cunning Survivor) or activated (Blockade Runner). Some spells also grant a creature unblockability, often along with shroud. Additionally, some effects that grant unblockability may only target creatures with power 2 or less (Dwarven Warriors). The latter version is nicknamed tunneling.

Spells and Artifacts that grant Unblockable
Enchantments

target creature
 * Aqueous Form  (Also grants scry 1 when enchanted creature attacks)
 * Cloak of Mists
 * Protective Bubble  (also has shroud)
 * Steel of the Godhead  (as long as enchanted creature is blue)
 * Tricks of the Trade</c>
 * Way of the Thief</c> (as long as you control a Gate)
 * Writ of Passage</c>  (enchanted creature with power 2 or less)

Instants


 * Hearth Charm</c>  (target creature with power 2 or less)
 * Infiltrate</c>
 * Sewers of Estark</c>
 * Teleport</c>
 * Trailblazer</c>
 * Veil of Secrecy</c>  (also grants shroud)

Sorceries
 * Artful Dodge</c>
 * Distortion Strike</c>
 * Ghostform</c>  (up to two target creatures)
 * Teleportal</c>, Overload
 * Touch of Invisibility</c>

Artifacts
 * Glaring Spotlight</c>  (, Sacrifice Glaring Spotlight, also gain hexproof)
 * Runed Arch</c>  (target creature(s) with power 2 or less)
 * <c>Tawnos's Wand</c>  (target creature with power 2 or less)
 * <c>Key to the City</c>  (undefined, Discard a card: Up to one target creature can't be blocked this turn)
 * <c>Manifold Key</c>  (, undefined: Target creature can't be blocked this turn)

Equipment
 * <c>Whispersilk Cloak</c>  (also grants shroud)

Land
 * <c>Rogue's Passage</c>, undefined: target creature is unblockable this turn

Cards that allow a player to block an unblockable attacking creature
Instants
 * <c>Choking Vines</c>
 * <c>Curtain of Light</c>
 * <c>Dazzling Beauty</c>
 * <c>Fog Patch</c>

Creature
 * <c>Trap Runner</c>  (activated ability)

"Cannot be blocked (except) by"
A variant of 'unblockable' restricts unblockability to a certain subset of creatures, often naming a color, creature type, number of power or greater, number of blocking creatures or creatures with a certain keyword ability.

Creatures that are "Cannot be blocked (except) by"
Cannot be blocked by [color]
 * <c>Barrenton Cragtreads</c>  (red)
 * <c>Dauthi Horror</c>  (white)
 * <c>Elder Spawn</c>  (red)
 * <c>Fylamarid</c>  (blue)
 * <c>Metathran Transport</c>  (blue)
 * <c>Mudbrawler Raiders</c>  (blue)
 * <c>Raven's Run Dragoon</c>  (black)
 * <c>Sacred Knight</c>  (black and/or red)
 * <c>Sootwalkers</c>  (white)
 * <c>Wanderbrine Rootcutters</c>  (green)

Cannot be blocked by artifact creatures
 * <c>Argothian Pixies</c>
 * <c>Basalt Golem</c>
 * <c>Clockwork Steed</c>

Cannot be blocked by creature tokens
 * <c>Legion Loyalist</c>

Cannot be blocked except by [color or artifact creatures]
 * <c>Amrou Seekers</c>  (artifact and/or white)
 * <c>Dread Warlock</c>  (black)
 * <c>Manta Ray</c>  (blue)
 * <c>Prowling Nightstalker</c>  (black)
 * <c>Skirk Shaman</c>  (artifact and/or red)
 * <c>Zulaport Enforcer</c>  (black)

Cannot be blocked by [creature type]
 * <c>Bog Rats</c>  (Walls)
 * <c>Clockwork Swarm</c>  (Walls)
 * <c>Flow of Maggots</c>  (non-Walls)
 * <c>Juggernaut</c>  (Walls)
 * <c>Otarian Juggernaut</c>  (Walls)
 * <c>Rampart Crawler</c>  (Walls)
 * <c>Stromkirk Noble</c>  (Humans)
 * <c>Vindictive Mob</c>  (Saprolings)

Cannot be blocked except by [creature type]
 * <c>Deathcult Rogue</c>  (Rogues)
 * <c>Evil Eye of Orms-by-Gore</c>  (Walls)
 * <c>Shifting Sliver</c>  (Slivers; grant by all Slivers)

Cannot be blocked by creatures with [keyword ability]
 * <c>Gnat Alley Creeper</c>  (flying)
 * <c>Greater Stone Spirit</c>  (flying)
 * <c>Stone Spirit</c>  (flying)
 * <c>Taoist Mystic</c>  (horsemanship)
 * <c>Zuo Ci, the Mocking Sage</c>  (horsemanship)

Cannot be blocked except by creatures with [keyword ability]
 * <c>Elven Riders</c>  (Walls and/or creatures with flying)
 * <c>Noggle Bandit</c>  (defender)
 * <c>Orchard Spirit</c>  (flying or reach)
 * <c>Signal Pest</c>  (flying or reach)
 * <c>Silhana Ledgewalker</c>  (flying)
 * <c>Spire Tracer</c>  (flying or reach)
 * <c>Treetop Rangers</c>  (flying)
 * <c>Treetop Scout</c>  (flying)

Cannot be blocked by more than [number of blocking creatures]
 * <c>Charging Rhino</c>  (one creature)
 * <c>Huang Zhong, Shu General</c>  (one creature)
 * <c>Ironhoof Ox</c>  (one creature)
 * <c>Krosan Vorine</c>  (one creature)
 * <c>Norwood Riders</c>  (one creature)
 * <c>Stalking Tiger</c>  (one creature)
 * <c>Yuan Shao, the Indecisive</c>  (one creature)

Cannot be blocked except by [number of blocking creatures]

two or more creatures (Menace)
 * <c>Caterwauling Boggart</c>  (grant by Goblin or Elemental you control)
 * <c>Horde of Boggarts</c>
 * <c>Kederekt Creeper</c>
 * <c>Ripscale Predator</c>
 * <c>Searing Spear Askari</c>  (activated ability)
 * <c>Stormblood Berserker</c>
 * <c>Summit Apes</c>  (active as long as controlling a Mountain)
 * <c>Terror of Kruin Pass</c> (grant by Werewolf you control)
 * <c>Two-Headed Dragon</c>
 * <c>Two-Headed Sliver</c>  (grant by all Slivers)
 * <c>Viashino Runner</c>
 * <c>Vine Kami</c>
 * <c>Wind Spirit</c>

three or more creatures
 * <c>Gorilla Berserkers</c>
 * <c>Guile</c>
 * <c>Pathrazer of Ulamog</c>
 * <c>Phyrexian Colossus</c>

Cannot be blocked by creatures with [number of power] or greater
 * <c>Amrou Kithkin</c>  (power 3)
 * <c>Daxos of Meletis</c>  (power 3)
 * <c>Fleet-Footed Monk</c>  (power 2)
 * <c>Goldmeadow Dodger</c>  (power 4)

Cannot be blocked by creatures with greater power (Skulk)
 * <c>Farbog Revenant</c>
 * <c>Fogwalker</c>
 * <c>Forgotten Creation</c>
 * <c>Furtive Homunculus</c>
 * <c>Pale Rider of Trostad</c>
 * <c>Persistent Nightmare</c> (back side of <c>Startled Awake</c>)
 * <c>Rancid Rats</c>
 * <c>Uninvited Geist</c>
 * <c>Vampire Cutthroat</c>
 * <c>Wharf Infiltrator</c>

Cannot be blocked by creatures power [number of power] or less
 * <c>War-Name Aspirant</c>  (power 1)
 * <c>Scuttling Doom Engine</c>  (power 2)
 * <c>Ghirapur Guide</c>  (power 2, granted by activated ability)
 * <c>Elegant Edgecrafters</c>  (power 2)
 * <c>Demolition Stomper</c>  (power 2)
 * <c>Outland Boar</c>  (power 2)
 * <c>Greater Sandwurm</c>  (power 2)
 * <c>Rhonas's Stalwart</c>  (power 2, on exert)

Spells and Artifacts that grant "Cannot be blocked (except) by"
Cannot be blocked by [color]
 * <c>Black Scarab</c>  (black)
 * <c>Blue Scarab</c>  (blue)
 * <c>Green Scarab</c>  (green)
 * <c>Red Scarab</c>  (red)
 * <c>White Scarab</c>  (white)

Cannot be blocked by artifact creatures
 * <c>Artifact Ward</c>

Cannot be blocked except by [color or artifact creatures]
 * <c>Seeker</c>  (artifact and/or white)

Cannot be blocked by [creature type]
 * <c>Blazing Torch</c>  (Vampires or Zombies)
 * <c>Field of Reality</c>  (Spirits)
 * <c>Tower of Coireall</c>  (Walls)

Cannot be blocked except by [creature type]
 * <c>Cloak of Invisibility</c>  (Walls) (also has phasing)
 * <c>Invisibility</c>  (Walls)

Cannot be blocked by creatures with [keyword ability]
 * <c>Dust Corona</c>  (flying)
 * <c>Skyblinder Staff</c>  (flying)

Cannot be blocked except by creatures with [keyword ability]
 * <c>Canopy Cover</c>  (flying or reach)
 * <c>Infiltrator's Magemark</c>  (defender)
 * <c>Treetop Bracers</c>  (flying)

Cannot be blocked by more than [number of blocking creatures]
 * <c>Alpha Authority</c>  (one creature, also has hexproof)
 * <c>Familiar Ground</c>  (one creature)
 * <c>Vorrac Battlehorns</c>  (one creature)

Cannot be blocked except by [number of blocking creatures]
 * <c>Goblin War Drums</c>  (two or more creatures)
 * <c>Imposing Visage</c>  (two or more creatures)
 * <c>Madcap Skills</c>  (two or more creatures)

Cannot be blocked by creatures with [number of power] or greater
 * <c>Kithkin Armor</c>  (power 3)

Cannot be blocked by creatures with greater power (Skulk)
 * <c>Behind the Scenes</c>
 * <c>Skeleton Key</c>

Rules
undefined