What are Death's stats for the “Chess with death” haunt in Betrayal at the House on the Hill?
I assume you're referring to Haunt 37, titled Checkmate

As per the REVISED Traitor's Manual, Death has a Knowledge of 8 (and it cheats). It has no other stats, and cannot be attacked by any means. As per the (revised) Survivor's Handbook, Each Holy Seal token removes one die (two in 3- or 4-player games) from all subsequent knowledge rolls by Death. (in a 5-player game, the effective minimum knowledge for Death is 3, while in smaller games, it is possible for Death to be forced to take a 0 on the roll).