When a player dies a Zombie will spawn in there place. I'd also appreciate it if you could have a config so you can decide if this only happens at night or not.
That's basically one line of VariableTriggers. Trigger event playerdeath + Entity ZOMBIE 1 <triggerloc> If I recall correctly, you cannot check day or night with VT, but you can check the light level.
Can also be easily done with OtherDrops, which can actually be locked to only happen at night and not just light levels.
Do you know how to code? If you do, then just make a Zombie entity replace the Person's entity on the EventHandler PlayerDeathEvent. Do NOT use PlayerRespawnEvent, because it will spawn a Zombie at a different location where the player respawns. You wouldn't want that! xD