After swallowing that special centipede and toad, Deun Yu gained immunity to all of the various poisons he was exposed to during the remainder of DGSD. He encountered a wide variety of poisons, each of which was unrelated to the others, so his immunity was widely-encompassing.
Was it *all* encompassing, however? Did the centipede and toad provide him complete immunity to all poisons that could ever exist in the world? I wonder if his immunity would have been effective against the poisons that showed up later in the Jin Yong world (i.e. West Poison Au Yeung Fung's poisons, Passion Flower poison from ROCH, the poisons used by Wu Ching Ngau's wife in HSDS, the poisons that afflicted Ling Wu Chung in SOD, etc.).