Despite how strongly some people might argue, there was never an arcade version of Splatterhouse 2. It's a myth.
To avoid comparisons between hero Rick Taylor and 'Friday The 13th' villain Jason Voorhees, the design of the Terror Mask in this game has been changed to appear less like a hockey mask and more like a skull.
The US manual for Splatterhouse 2 mentions secret doorways and passageways. However there are none to be found in the game. The only doors that appear, which cannot be entered, are in the sewers of stage 2. This was just a feature of a prototype version used at the time the manual was written.