Someone who people don't know much about or how they will perform.
They chose a dark horse candidate for president.
Dial Down a Notch:
To relax, chill out, de-escalate.
Whoa, you're so hyper! Dial it down a notch.
Down To The Wire:
Very little time is left. (See: Crunch time)
We’re really down to the wire now. Let’s get everything done.
Drink like a fish:
To drink a lot at one time (alcohol).
Jack really knows how to drink like a fish!
Dropping Like Flies:
People getting sick, exhausted or dying.
Unreal! Our players are dropping like flies out there!