First Strike is a creature ability that adds another combat damage step. Creatures with first strike will do damage to a creature without first strike, first. Basically, a 2/2 with First Strike was blocked or was being blocked by a 2/2 without First Strike, the creature without First Strike would not even be able to damage the one with First Strike.
A good combination would be adding First Strike and Deathtouch. The creature will do damage first (assuming the blocking creature does not have first strike) and since Deathtouch is destroys the creature when damaged, the defending/attacking creature will be destroyed instantly.
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