Deathtouch is a static ability that changes what counts as lethal damage. Under CR 702.2b, a creature with deathtouch causes any nonzero amount of damage it deals to a creature to be considered lethal damage. This overrides the normal rule that a creature is destroyed only when damage meets or exceeds its toughness.
The normal rule (CR 704.5g) destroys a creature when it has damage marked on it equal to or greater than its toughness. Deathtouch modifies this via CR 702.2c: damage from a deathtouch source is always sufficient to destroy, even if it is only 1 damage against a 5-toughness creature.
It is important to note that deathtouch does not reduce toughness — it simply makes any damage from the source lethal. State-based actions will then destroy the damaged creature the next time they are checked, even though the damage (1) is less than the toughness (5).
Example: Your 1/1 Typhoid Rats (deathtouch) blocks your opponent's 5/5 Colossal Dreadmaw. Combat damage is dealt: Typhoid Rats deals 1 damage to the Dreadmaw. Even though 1 is far less than 5, state-based actions destroy the Dreadmaw because it received damage from a deathtouch source. The Rats also die to the 5 damage in return.
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.