Yes, ENDEMICAL is a Scrabble word!

Letter values in Scrabble US: E 1, N 1, D 2, E 1, M 3, I 1, C 3, A 1, L 1.

Is it a valid word?

ENDEMICAL is a valid word in the official Scrabble dictionary (US) and the UK Scrabble Dictionary, but not in Words with Friends (ENABLE).

of or relating to a disease (or anything resembling a disease) constantly present to greater or lesser extent in a particular locality