Syththunu is a Great Old One (Dark Giant) created by DC Comics which appeared in the 6-part Eclipso Rising story arc with its first appearance in 2011 in issue #54 of Volume 2 of the Justice League of America comic series.
Synththunu is an Elder God, who at one time was feared and revered on Earth. It's dark power was respected by the Atlantean Mage Arion. He was Imprisoned in a crystal small enough to be held in the palm of a man's hand. Whom was awakened and released by Eclipso in the early 21st century. An intelligent god whom Eclipso communicated with and participated in Eclipso's assault on Emerald City which fell within a quarter hour.
The Elder God's form is that of a 100+ ft tall humanoid squid with a humanoid torso on top of tentacles, two clawed hands with 4 fingers each and tentacles on lower part of the face. Alongside Eclipso and others he recruited or enthralled, Synththunu battled the Justice League of America on the surface of the moon, using its arms and lower tentacles (which could stretch great lengths).