The top spin has the dubious honour of being simultaneously the most powerful, and the most broken weapon in the series. Due to really sloppy coding and invincibility timers and collision detection, half the time it'll do a one-hit kill and the rest of the time you'll do basically no damage and use up all your ammo. Gamma and Shadow man are weak to it, though, in-game, it's a lot safer to just use the Search Snake (it's alternate weakness).