You are correct. You suggested scouting with Theryndil, but Keia's follow up message said Amanu was in the rear, so I must have assumed Erenal was scouting. Okay, consider your positions switched.
Marcus has never heard of a behir with multiple heads, but then who knows what being a half-dragon might do to a creature?
The creature moves another twenty feet towards the nomad and the southern end of the island. Despite Theryndil's attempts at evasion, the beast still seems to be heading his direction. Six heads are now visible, most of them straining forward.
But one head continues to weave watchful patterns. Marcus is almost at the shore when that head swings in his direction, pauses, and lets out a roar. The other heads swing to the east, and the creature begins charging in Marcus' direction.
Initiatives: Theryndil 17, Arramor 12, Amanu 10, Marcus 8, Erenal 5. Actions, please.