Greatwyrm

Greatwyrms were dragons that had achieved godlike abilities, approaching the powers of the aspects of Tiamat and Bahamut.

Abilities
Though exact powers varied with each type of greatwrym, in general all greatwyrms had abilities that allowed them to return to near-full strength just before death. Many of their other abilities were more powerful versions of those of normal dragons, with chromatic greatwryms being able to make spears out of arcane power, metallic greatwyrms being able to drain the energy of foes, and gem greatwyrms having more powerful psionics.

Creation
According to Fizban the Fabulous (one of Bahamut's aspects), greatwryms were normally created when ancient dragons, usually at least twelve centuries old, ate or ritually merged with their "echoes" from other worlds, or consumed their energies in other ways.

Notable Greatwyrms

 * Sardior's greatwyrms were a group of five greatwyrms (one of each of the five types of gem dragons) who intended to absorb every one of their echoes with the ultimate goal of coming together and reforming Sardior.