There is also a randomly triggered Hercules Rage feature that can destroy all Hydra! This is exactly the same as The Incredible Hulk's Smash Bonus feature, and you can also trigger the Hulk Rage feature!
When the Hercules wild symbol appears in the middle of the third reel, the Herculean Strength function will appear - it will expand to give you 2 respins with a locked extension field. If you get Hercules Wild on 3 intermediate reels, it will unfold on all 3 reels, including 1 respin and a locked extension field!