[Hated Trope] Using a character's intended "weakness" actually makes the fight harder/more annoying.

Shadow Man (Megaman 3) - Megaman, as a franchise, also has a large focus on exploiting weaknesses, as each Robot Master boss is weak to the weapon of another Robot Master. While some weapons are obviously better than others, usually using a weakness weapon will make the fight easier. In the case of Shadow Man, this isn't the case. Shadow Man, as a boss, is a very mobile fighter capable of rushing down the player with his speed and keeping a distance with his Shadow Blade. However, if you just have a good eye and keep a good distance, he isn't that bad with some practice. The issue comes down to using his weakness weapon, the Top Spin, a close-range melee attack with pitiful range, while the Top Spin does massive damage to Shadow Man, the combination of his speed, collision damage, and the general unwieldy nature of the Top Spin can make the fight much more annoying than just doing it with the Mega Buster.