I think Ultra Humanite was hinted at in episode 2 (the large shadowy beast in the cage).
And add me as a 3rd vote for finding this show to be an absolute joy. Brec Bassinger and Luke Wilson's portrayals are dynamite, and I love love love that it's leaning so hard into JSA lore.
(Real JSA lore, not JSA-lite like we got in Legends of Tommorrow).