Yes, EFFICACIOUS is a Scrabble word!

Letter values in Scrabble US: E 1, F 4, F 4, I 1, C 3, A 1, C 3, I 1, O 1, U 1, S 1.

Is it a valid word?

EFFICACIOUS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

marked by qualities giving the power to produce an intended effect
producing or capable of producing an intended result or having a striking effect