Spawn is technically dead, and effects that normally work on living creatures have little or no effect on him. Spawn's power comes from what he wills his necroplasmic suit to do. In the issues before the monumental issue 50, Spawn had a limited power supply or 9999. Each time Spawn used his energy, the counter would drain. In issue 50 Spawn drains his power completely to help Terry Fitzgerald recover from an unknown illness.
Post issue 50, Spawn's power is endless. There was even a brief period after issue #100 where Spawn was practically a god. At the time no one was able to harm him in any way. Anything Spawn wills his necroplasmic suit to do, will happen. Spawn has altered his physical appearance at times, and his body is a living weapon. His suit even "matures", by morphing into different variations. The most noteable changes being the "Raven" suit, in which his power was at its highest. He is able to transform any part of his suit and/or body into whatever he sees fit for the current situation. Spawn's suit is a living organism, able to feel pain. Spawn does not need to eat or sleep. The only human characteristics Spawn retains now are his emotion and the ability to feel pain...he does not grow tired, feel fatigue, or even need to breathe. Should Spawn be injured while in battle, his suit is the one to feel the blow, as a result, if his suit is severely injured, Spawn may be rendered helpless. He is also abnormally strong, seemingly able to lift/move anything that he needs moved. Aside from abnormal strength and his necroplasmic suit, Spawn is able to concentrate necroplasma and shoot it in an energy like "beam" from any part of his body. Though he's only shot it out of his hands, and from a hole he made in his chest in the comics. He is also able to manipulate reality and use mental powers to subdue enemies. For instance, after defeating a robot known as "Overtwar", Spawn cornered Jason Wynn, and "ripped" all the skin from Jason's body. At least, that is what Jason's mind thought, proving that Spawn has an infinte array of power, able to do anything he can will his mind and suit to do.