What about something like a storm cloud combining water and electricity? It could require all four water and electricity cantrips currently out.

Examples:
You gesture and a small dark cloud begins to form over Person?s head. The cloud seems to swell just as fat water droplets begin to splash down on Person.

A bolt of lightning erupts from a small dark cloud and strikes Person, who jerks reflexively.

A small dark cloud dissipates as suddenly as it appeared.

Sinah