The phrase "a double-edged/two-edged sword" refers to something that has both positive and negative effects. There are several synonyms that can be used in place of this idiom, including "a mixed blessing," "a two-faced coin," and "a catch-22." "A mixed blessing" implies that something has both benefits and drawbacks, just like a double-edged sword could cut in two directions. "A two-faced coin" references how something can appear one way on the surface but have hidden consequences, like a sword's blade having two sharp edges. Finally, "a catch-22" refers to a situation in which someone is in a dilemma or is stuck between two undesirable options, which is similar to the danger of a double-edged sword.