The main character is a hero with supernatural qualities.
The Hero is Tested
The Hero is charged with a Quest
"You worked at your folly for seven nightfalls" (lines 516-517). Beowulf swam for seven days.
The Hero Travels to a Supernatural World
"I was greater in swim-strength gliding through waves longer in arm-strokes than my lagging friend" (lines 533-534). Beowulf is explaining how Unferth's story isn't true.
The Hero's Low Point
"I swore to myself when I sailed from home mounted my ship with men around me that I alone would ease your heartgrief settle this feud here or fall deathwards in Grendel's grasp"(lines 632-636) Beowulf says he will kill Grendel for the Danes
"In that hell-murky mere many a snake-creature curious water worms cut through the gore on the hard bank-slopes black fiends were roiling serpents and mere-sprites slid along the rock by cold morninglight" (lines 1425-1429). Beowulf is at Grendel's Mother's lair.
"She clamped his arms in her cold fiendgrip returned his tugging with claw-fingers she toppled him over with towering strength raging with fire-eyes" (lines 1541-1544) Grendel's mother is about to kill Beowulf.