Without speaking, and seeing the creatures abovedeck defeated, he runs below the deck to face the other foes. Seeing them- and the enormous tentacle- he swiftly raises his staff and points it towards their foes, firing a mass of kelpy tentacles in response.
SpoilerKelpstrand. Rolls OOC.
Also, Knowledge (Nature) to identify the things or the tentacle.
Things: (1d20+13)[23]
Tentacle: (1d20+13)[32]