Deathtouch is a keyword ability that makes any amount of damage dealt by its source lethal to a creature. This makes even a 1/1 creature with deathtouch an unpleasant proposition to block with something much larger.
Basilisk Collar can give deathtouch to creatures that repeatedly deal small amounts of damage, while Hooded Blightfang provides additional rewards for attacking with deathtouch creatures. Deathtouch also pairs particularly well with trample.