Deathtouch

Deathtouch is a static ability that causes damage dealt by an object to be especially effective against creatures.

Description
Similar abilities to deathtouch, always triggered, had been spelled out on earlier creatures, the earliest being Thicket Basilisk from Alpha, hence R&D's pre-keyword name for the ability being "basilisk". The keyword was introduced in Future Sight, as a preview for Lorwyn, in which it featured more prominently. Technically, it gained evergreen status with Tenth Edition but was first featured in a core set with Magic 2010. At the time of keywording it was still a triggered keyword ability; it changed to its current status as a static ability associated with a new state-based action with Magic 2010 and new damage assignment rules with Magic 2011.

This ability was primary in both black and green for a while. Its now secondary in green, because R&D found that black both had more need for it and had more flavorful ways to express it creatively. Now that deathtouch is keyworded, R&D no longer creates variants.

Ikoria: Lair of Behemoths introduced deathtouch counters.

Rulings

 * If a creature (whether it has deathtouch or not) blocks or is blocked by multiple creatures, those creatures must be put into damage assignment order during the declare blockers step. The creature then assigns its combat damage to those creatures according to the damage assignment order announced for it. It can't assign combat damage to one of those creatures unless each creature that precedes that creature in its order is assigned lethal damage. If a creature with deathtouch blocks or is blocked by multiple creatures, everything works exactly the same way with one exception: assigning even 1 of that creature's damage to a creature is considered to be lethal damage.
 * Example: The damage assignment order of an attacking Acidic Slime (a 2/2 creature with deathtouch) is Spined Wurm (a 5/4 creature) then Siege Mastodon (a 3/5 creature) then Runeclaw Bear (a 2/2 creature). Acidic Slime can assign 1 damage to the Wurm and 1 damage to the Mastodon, or 2 damage to the Wurm. It can't assign damage to the Bear. Each creature Acidic Slime deals damage to is destroyed.
 * If an attacking creature with deathtouch and trample becomes blocked, the attacking creature first assigns damage to the creature(s) blocking it. Once all those blocking creatures are assigned lethal damage, any remaining damage is assigned as its controller chooses among those blocking creatures and the player or planeswalker the creature is attacking. However, since the creature has deathtouch, assigning even 1 damage to a creature is considered to be lethal damage.
 * Example: Yavimaya Wurm (a 6/4 creature with trample) is equipped with Gorgon Flail</c> (an Equipment that grants the equipped creature +1/+1 and deathtouch). It attacks a player and is blocked by Siege Mastodon</c> (a 3/5 creature). Yavimaya Wurm</c> must assign at least 1 damage to the Mastodon. Its remaining damage may be assigned as its controller chooses between the Mastodon and the defending player. Notably, the Wurm may assign 1 damage to the Mastodon and 6 damage to the defending player. After that damage is dealt to the Mastodon, the Mastodon will be destroyed.
 * If a creature with deathtouch and another creature both block or are blocked by a creature, the other creature may take into account the fact that any combat damage dealt by a creature with deathtouch is considered to be lethal damage.
 * Example: An attacking Acidic Slime</c> (a 2/2 creature with deathtouch) and an attacking Yavimaya Wurm</c> (a 6/4 creature with trample) are both blocked by a Palace Guard</c> (a 1/4 creature that can block any number of creatures). The Slime must assign its 2 damage to the Guard. Since the Guard is being assigned lethal damage, the Wurm's 6 damage may be assigned as its controller chooses between the Guard and the defending player. Notably, the Wurm may assign all 6 damage to the defending player. It doesn't matter which creature's damage is assigned first, as long as the final damage assignment follows all the applicable parameters.
 * A regeneration effect can save a creature that's been dealt damage by a source with deathtouch.
 * If multiple state-based actions would destroy a creature at the same time (because it's been dealt lethal damage and been dealt damage by a source with deathtouch), a single regeneration effect will replace all of them and save the creature.
 * If a creature is dealt damage by a source with deathtouch, it'll be destroyed as a state-based action. That means there's no time to react between the time the creature is dealt damage and the time it's destroyed. If you want to put a regeneration shield on it, or sacrifice it for some effect, or anything else, you must do so before the damage is actually dealt.
 * The rules that care about deathtouch function no matter where the source with deathtouch is. In other words, if a spell or ability causes a card with deathtouch that's not on the battlefield to deal damage to a creature (like Selfless Exorcist</c>'s ability does, for example), that creature will be destroyed. This isn't the same as damage dealt by a source that has changed zones; see below.
 * If a source of damage hasn't changed zones by the time that damage is dealt, its characteristics are checked to see if it has deathtouch at that time. If the source has changed zones by then, its last existence in the zone it was expected to be in is checked to see if it had deathtouch at that time.

Cards that grant Deathtouch
Creatures
 * Ankle Shanker</c> (When it attacks, creatures you control gain deathtouch and first strike until end of turn)
 * Drunau Corpse Trawler</c> (: Target Zombie)
 * Felhide Petrifier</c> (Minotaurs you control)
 * Nightshade Peddler</c> (Creature Soulbond with it)
 * Onyx Mage</c> (: target creature until end of turn)
 * Ogre Slumlord</c> (Rats you control)
 * Painsmith</c> (Whenever you cast an artifact spell)
 * Paragon of Open Graves</c> (, undefined: Another target black creature you control until end of turn.)
 * Pestilent Spirit</c> (Instant and Sorcery spells you control)
 * <c>Sydri, Galvanic Genius</c> (: Target artifact creature gains deathtouch and lifelink until end of turn.)
 * <c>Wasteland Viper</c> (, discard to grant deathtouch to attacking creature)

Enchantments
 * <c>Gift of the Deity</c> (as long as enchanted creature is black)

Instants
 * <c>Necrobite</c>
 * <c>Serpent's Gift</c>
 * <c>Willing</c>

Artifacts
 * <c>Basilisk Collar</c> (and Lifelink)
 * <c>Gorgon's Head</c>
 * <c>Vial of Poison</c> (, sacrifice to grant deathtouch)

Enchantment Creatures Enchantment Artifacts
 * <c>Archetype of Finality</c> (all creatures you control, and remove it from all creatures your opponents control)
 * <c>Baleful Eidolon</c> (if cast as an Aura for its bestow cost of )
 * <c>Bow of Nylea</c> (attacking creatures you control)

Cards that remove Deathtouch

 * <c>Archetype of Finality</c> (from creatures your opponents control, your creatures gain deathtouch)

Plane card that grants Deathtouch

 * <c>Onakke Catacomb</c> (all creatures)

Trivia

 * Deathtouch was featured as rules card 3 of 9 in the Magic 2011 set.
 * The deathtouch counter of Ikoria: Lair of Behemoths was the only counter from that set to feature a symbol that differed from the one used in MTG Arena.