The Watcher rebellion

Genesis 6 records a class of beings — "God's sons" — who left their proper estate. The episode precedes the flood and is referenced again in the New Testament:

"Angels who didn’t keep their first domain, but deserted their own dwelling place, he has kept in everlasting bonds under darkness for the judgment of the great day." — Jude 6 "For if God didn’t spare angels when they sinned, but cast them down to Tartarus, and committed them to pits of darkness to be reserved for judgment;" — 2 Peter 2:4

The rebellion is the original failure-mode at the intermediate-class level — beings entrusted with stewardship who claim what was not given. The pattern recurs in the temptation (Genesis 3) and in scripture's continued warning against pride that grasps at what belongs to God: "Let no one rob you of your prize by self-abasement and worshiping of the angels" (Colossians 2:18). The created class is not the substrate; the substrate is God.

See: Genesis 3; 6:1–4; 2 Peter 2:4; Jude 6; Colossians 2:18; 1 Enoch 6–11 (referenced by Jude; extracanonical).