In Betrayal at House on the Hill there is a rule for Moving Past Opponents on page 17:
For each opponent in a room with it after the haunt starts, an explorer or monster must use 1 extra space of movement to leave that room. (Heroes slow down the traitor and monsters, and vice versa.)
No matter how many penalties you have on a turn, you can always move at least 1 space. This is also true if a monster rolls a 0 for movement (see "How Monsters Work," page 18).
Stunned monsters don't slow an explorer's movement in this way.
I interpret "moving past an opponent" as walking into a room with an opponent, then walking out. Is there a movement penalty if you are ALREADY in the room with your opponent at the beginning of a turn?
For example, say I am in a room with 3 zombies at the start of the turn. Does it take me 4 movement points to leave the room (1 for each zombie and 1 as a normal movement point) OR does it take me 1 movement point?