Elena was a mermaid and had managed to get separated from their group having wandered off, they were now lost but continued to explore around, unintentionally wandering into siren territory, unbeknownst to them that Damon lurked around, watching Elena carefully, deciding to approach them slowly as to not scare them

"Never seen you around here before"

He spoke softly trying not to scare them, cranking his chant subtly to disorient the poor mermaid further