To dream that you are a superhero represents your above-average talents, ideas, and other hidden abilities that you may not realise you possessed. Alternatively, the dream parallels some extraordinary problem or issue that you are trying to deal with in your waking life. You need to approach the issue head on.
To dream that a superhero has weak powers suggests that no one is invincible; everyone has their weaknesses. This superhero in your dream may represent someone in your waking life who you idolise and who you thought was always so strong. Perhaps this person disappointed you or this person suddenly fell ill.