Ekhidnas can be found at Skellige.
They are weak against Grapeshot, Hybrid Oil, Igni and Aard.
On the ground, however, they are virtually defenseless, and so a wise tactic is to damage their fin-like wings to force them to land. The Igni Sign also proves effective when fighting against them. Threatened or injured sirens will let out a terrifying shriek, leaving their opponents stunned while they escape — and their sisters swoop down for an easy attack.