well in your repop code where it says for(var/blah) make it specific like: for(var/mob/Monster/M)
if(M:Respawn)
blah..


mob/Monster
var/Respawn = 1

var/list/types=list(/mob/poop/,/mob/dog/)
mob/var{respawn=0;sx=0;sy=0;sz=0}
mob/Del()
if(src.respawn)
sleep(20)
new src.type(src.sx,sy,sz)
..()
mob/New()
if(types.Find(src.type))
src.respawn=1
src.sx=src.x
src.sy=src.y
src.sz=src.z

That's an example.

If you ask a general question like that, be prepared to get responses that don't fit into your current system. If you want specific help, you should actually post some of your code so that people can see how your system currently works, and adapt their examples to fit.