Yes, TRICKSTERS is a Scrabble word!

Letter values in Scrabble US: T 1, R 1, I 1, C 3, K 5, S 1, T 1, E 1, R 1, S 1.

Is it a valid word?

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

someone who plays practical jokes on others
someone who leads you to believe something that is not true
a mischievous supernatural being found in the folklore of many primitive people; sometimes distinguished by prodigious biological drives and exaggerated bodily parts

Also: cut-up, practical joker.