Mummie, which is now in its Titan form, pulled out the scythe that the Horseman of Death uses. Since the scythe has been pulled out, the dark dragon king is no longer being tainted at an alarming rate. The strange miasma is still present in his body, but it is no longer progressing faster than before.
The dark dragon king grunted and its body that is getting tainted with the strange miasma suddenly exploded in energy. One of the magics that dragons with the darkness attributes uniquely possess is called Elemental Devour. Dark dragons could easily swallow any attacks or energy of a different element into their body and turn it into energy.
With the dark dragon king no longer being corroded at an astonishing pace, the dark dragon king managed to activate this ability and instantly turned the strange miasma into its energy. The conversion is not complete though as there are still signs that the dark dragon king is infected with the strange miasma albeit at a miniscule amount.