Some of the most ferocious characters from the Negative Zone are imbued with the "Opposing Force" or "The Essence".
In the Annihilation Story Arc, this power is seen imbued in the Seekers and their leader: Ravenous.
For the Seekers and Ravenous, their bodies are the conduits of the power which actually resides in creatures called Currs. They tether themselves to the Currs to take advantage of the Opposing Force.
If separated from their Currs or if the Currs are destroyed, regeneration is quick.
From the battles within the Annihilation story, in a one-on-one battle, the one imbued with the Power Cosmic seems to have the advantage against one imbued with the Opposing Force (see the Silver Surfer vs. Ravenous image).
In a one-to-many (Power Cosmic - to - Opposing Force), there is a clear advantage to the ones imbued with the Opposing Force (see Terrax vs. Seekers).