" The Ultimate Weapon " (Funimation/Toonami). Saga: Part of the Android Saga (Season 4).
This episode is often cited by fans as the moment the threat level shifts from Dr. Gero’s "energy absorption" models to the far more powerful and unpredictable "infinite energy" models that Trunks feared. Android 18 fight that follows? Goodbye Doctor Gero! - Dragon Ball Z Episode 134 Reaction Dragon Ball Z (Dub) Episode 134
Dr. Gero is eliminated by his own creation, Android 17. " The Ultimate Weapon " (Funimation/Toonami)