Thank you, KeshaFilm! I suppose I'll have to stick to my anti-enemy stacking workaround. I'll check the manual more thoroughly about "map return", but I have to say that I find it hard to figure out, from the info in the manual, how to use scripts to make hazard blocks kill the player instantly. If anyone has the patience to explain, I'd be very grateful.
EDIT:
In case anyone else would have problems trying to do the same thing, I managed to get it working using triggers, like Kesha suggested, by putting using triggers instead of hazard blocks. I wrote the following in the script file:
player hurt 200
map quickreturn