A higher-than-normal metabolism- black mambas are well known for being more active than most snakes. They've also got a great deal of very effective venom. This is in addition to all the other adaptations that snakes have, eg, high flexibility and a skeletal structure that allows great leverage against both high surface areas (such as the ground) and low contact areas (such as tree branches), all the senses snakes (particularly poisonous snakes) have, eg, the ability to feel vibrations of the ground so acutely that no other aural sense is needed (snakes have no ears).
It is the fastest snake on earth (14 mph). It is very aggressive and doesn't give up on attacking back when it feels threatened. Instead of running away, it fights back, on and on, injecting poison with every bite, to kill the attacker or person. And is extremely highly poisonous.