Hello!
You can right click on the entity to edit the properties, in there you can set the amount of re-spawns and the time between re-spawns etc once that entity is destroyed, or script it:
In the destroy script of Guard 1, include the command Activateifused=1. In the properties of Guard 1 place the name of Guard 2 in the ifused box. In the properties of Guard 2 set the spawn at start to No.
(or you can continue the process for each Guard 3,4 etc)
You could also use a trigger zone to spawn a certain entity, say 2 guards in a room, when killed they will unlock the door leading to the next room where you could set up another trigger zone to spawn more guards/different guards.
In the trigger zone properties, add the name of the entity (guard 1 for example) to the ifused box, and change the script to plrinzoneactivateused.
;Artificial Intelligence Script
;Header
desc = Plr In Zone, activate entity specified in IF USED
;Triggers
:state=0,plrwithinzone=1:activateifused=1,sound=$0,state=1
:state=1,plrwithinzone=0:state=0
Then edit the properties of the Entity (or Guard 1) to spawn at start no, and spawn after delay yes.
Using trigger zones to spawn after delay rather than the start of the game will free up some processing and loading time of the game as well!