Eldrazi spawn squirmy, underdeveloped, mana-infused pupa. Eldrazi spawn are small - mere infants compared to the Brobdingnagian monstrosities they serve - but they serve an important role to the brood lineage. By some unknown process, greater Eldrazi can store consumed energy in their spawned underlings and then hatch greater Eldrazi by consuming the spawn in turn.
Each lineage has its own form of eldrazi spawn. Just like other Eldrazi, the anatomy and body plan of the spawn creatures follow the look of the rest of the lineage. The spawn of the Emrakul lineage walk on two stumpy little legs, and have some of the same bizarre coloration and spongy latticework of its lineage built into its anatomy.