Mortal table for more mortal folk you kill like nobles or dragons and planar one for beings from other planes like elves or demons or elementals.
So your players meet some other planar being. The mortal form it manifested is destroyed, and its spirit returns home. Once its true native form is complete, the entity will be quite miffy and embarrassed. Maybe higher-ups get involved when they report their failures. But such a sleight by mortal beings messing with the fate of superior beings cannot be just forgotten. Making a new body on the mortal plane may be limited a while, depending on the type. Greater beings find it harder but some specifically recover faster, like night hags.
In my more mythic games, monsters are the bitter venom of the gods and doing their job. Often they have a monster saved for some hero after causing enough suffering. Killing the monsters not at the right time makes the gods angry. Monsters and even bandits might have family. Turns out that bandit was a bastard of a high-ranking lord who feels obligated to kill the adventurers doing their duty. Supernatural parents might spy on their children or feel honour-bound to kill the killers of their spawn (or kill the killers' spawn).
Beef from the fancy bosses adventurers kill gives DM many fun opportunities. Enemies might not be obvious and act from afar. Perhaps those thugs you kill turn out to be the kin of the first guy you killed, and now the whole clan hate you, and you dont really know whats happening. They might decide their enemy should feel loss and suffer before dying. Perhaps take away the killers loved ones. Even if your poor and powerless just burn their house down or give all their grooming implements to some leppers then return them. Eventually, the tormenter will want to make a declaration and might overplay their hand against the adventurers. So when you kill this boss after a fight you just escalate to the next higher tier of a blood feud. A king or nation might have power used for revenge by trickery, forgery or bribery.
I like in Viking sorties like Burt Njarl the hero, estimates the legal consequences of attacking guys who hunt him. If he strikes first he could calculate how much money and cattle he would pay if he attacked first. But this is weighed up with, do I let a bunch of guys attack me first so It will cost less to kill them if they start it. Some factions might be paid off or the escalation of the fued limited. The origional angry person might refuse their boss declaring a fued over and may spilt ties or betray the boss. Perhaps the power and drive helps your victims kin gain more power and experience or even adventures.
Imps, sprites, pixies and similar beings can be great for petty revenge and can take a while to discover and kill.
The higher your level the more blood fueds you should have.
Perhaps every visit to civilisation or your domain should have trouble, from enemies.
"Honestly we had to take over a kingdom because of that guy I killed in a pub fight that led to assassins and fighting a noble clan, and then having to nobble the king"
d12 Planar Revenge Table
1 Try to form a new body and attack as quick as possible
d12 Petty Mortal Revenge Table
1 Creature has bitter orphans or kin
d12 Cheap Petty Revenge
1 Poisoning
d12 Rich Petty Revenge
1 Hire a bandit gang
2 Hire theives guild or gang thugs
3 Have foe declared outlaw or declared a traitor
4 Put out bounty, wanted posters or murder contracts
d12 Weird Cruel Revenge
1 Send mercenary kidnappers to kidnap the foe in a dungeon to be tortured for years by a famous torturer or perhaps in person
2 Send a mercenary force to kill and destroy the home and allies
4 Fake evidence to initiate a blood feud with a vindictive faction of psychos
5 Construct weird assassin order of fanatics obligated to never quit








