Diving into a body of water seems to message even when a person is invisible. This may be intended, but I don't think it's clear to the invisible person that they are outed by this action.

[PERSON I HAPPEN TO KNOW OOCLY IS A NECROMANCER] gracefully dives down from above, her arms relaxed along her sides.

She lands smoothly with barely a splash!

You notice a disturbance in the water moving sideways to the strong current.

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