I will never play a legacy, which is kind of the opposite of my playstyle, so what am I doing thinking up variations for it? To be fair, to make this a meaningful "royal" family you'd want to play a neighborhood around it.

For what it's worth:

Your founder will have one arbitrary trait, possession of which will limit eligibility for heirship, which has a reasonable but not guaranteed chance of expressing in each generation. The simplest is gender - if your founder is male, all heirs must be male; if your founder is female, all heirs must be female. Obviously you're not allowed to quit without saving until you get the desired gender. If you choose something else, you'd have to take steps to ensure the possibility of the trait expressing without guaranteeing it. If you choose blondness, for instance, you'd either limit spouse selection, or fiddle with the chosen spouse's genes. If you chose aspiration, you'd have to roll dice every time. And so on.

There are no heir polls. The line of succession is as follows: oldest legitimate child (keep track of which twin is born first, it matters!) who expresses the desired trait at the time of the "King's" death. If no legitimate children expressing the trait exist at that time, the heir is the oldest illegitimate child expressing that trait. In the absence of illegitimate children, look for the younger siblings (again preferring legitimate ones to illegitimate ones; half-siblings are fine as long as the shared parent is on the main line of succession) of the "King"

If the heir is not yet a full adult at the "King's" death, a regent must be assigned. This regent will be the person, related or not, who has the highest relationship with the "King" at the time of death (so pay attention to those relationship panels!). The regent will move into the household and act as head of family until the heir comes of age by growing to full adult (yes, YAs will have to drop out if they want to assume control immediately). If the relationship between the regent and the heir is friendly, the regent will be honest and step down when the heir comes of age. If it's negative, the regent will attempt to usurp the throne. If neutral, assign a percent chance of usurpation based on the Lifetime score of the regent toward the heir - i.e., if the regent has a 40 in the lower panel, there is a 60% chance of an attempt at usurpation. This is checked at time of move-in, but if between the time of move-in and the date the heir comes of age either friendship or enmity develops, these states will change the regent's intentions.

Usurpation is attempted by undermining the heir with the rest of the household. If, on coming of age, the heir's relationships with a simple majority of the household are not at least 20 points better each than the usurper's relationships with them, the heir is booted out. Pets, babies, and toddlers do not count for this total.

Yes, the regent can salt the household with his own friends and relations, but he can't tell anybody already in the household to move out. And yes, if a teen runs away, he's pretty much abdicated his throne. The regent can also create conditions which place the heir at risk, such as influencing him to fix things when his mechanical points are low, withholding comfort soup during an epidemic, blocking access to motive-boosting items and interactions, etc.

A regent who is also a potential heir (such as the next younger sibling of a "king" with only one eligible offspring) automatically becomes "king" after a successful usurpation; but a regent with no legal claim to the throne will either have to clear out all the potential heirs in the family one by one, or stage a coup by marrying the "king's" surviving spouse, defeating each adult legitimate potential heir in single combat at or before the time of the original heir's coming of age, or by some other ingenious method of your devising.

You could probably devise rules for rebellions and wars of succession, too, but let's keep this simple for now.

The challenge ends when someone inherits who is not a direct descendent of the original founder or who lacks the required trait. Give yourself ten points for every generation, subtract a point for every regency, subtract five points for every successful usurpation, subtract another point for every casualty of an usurpation attempt, add two points for every peaceful transfer of power after a regency, and that's your score. For whatever scores are worth to you.

The Arbitrary Trait: Your founder will have one arbitrary trait. The trait limits eligibility for heirship. For example, one "arbitrary" trait is gender. If your founder is male, then all heirs must be male; if your founder is female, all heirs must be female. In this case, you are not allowed to quit without saving, if the baby born is of the wrong gender. Doing so would be considered cheating.

Inheritance: There are no heir polls. The heir is to be selected by the following guideline.

Order	Line of Succession
1	Oldest legitimate child who expresses the desired trait at the time of the death of the Head of Household inherits. In the case of twins, the older twin inherits.
2	Oldest illegitimate child who expresses the desired trait at the time of the death of the Head of Household inherits. In the case of twins, the older twin inherits.
3	Oldest sibling or half-sibling, related by blood, of the Head of Household who expresses the desired trait at the time of the death of the Head of Household inherits.

Age of Heirship: At the death of the previous Head of Household

If the heir is a teenager or younger, then an older relative or friend of the family or an acquaintance may take control of the family property, but the rightful heir is the son or daughter by direct descent or some relative by blood lineage.

Heirship: If the relationship between the property caretaker and the heir is good (at least 50 Daily Relationship Score or Friend level), then the property caretaker may allow the rightful heir to the property. If the relationship between the property caretaker and the heir is bad (Enemy level), then the property caretaker may try to seize the property for his/her own. The exact details of how the player is going to play this out is up to the player.

If the relationship between the heir and the rest of the household is sour, then the heir is disqualified from heirship. The exact details of how the player is going to play this out or at which relationship score would count as "disqualified" is up to the player.

The property caretaker cannot order anybody else in the household to move out, including the heir.

If a teen runs away from home, then he/she is disqualified from heirship.

If the property caretaker is a relative to the Head of Household, then he/she is able to succeed to the Head of Household, provided that he/she defeats the rightful heirs before him/her in the line of succession. Another way is to marry the spouse of the Head of Household.

The Ending: The challenge ends when someone who is not a direct descendant of the original founder or who lacks the required trait inherits.

Scoring:

Points	Descriptions
+10	For each generation
-1	For each intervening property caretaker
-1	For every casualty of an usurpation attempt, if you happen to do a "battle" between two Sims to fight for the right to heirship of the property
+2	For every peaceful transfer of power

Feel free to add anything you want to this basic challenge!

Glossary:

Property: Anything that belongs to the Head of Household. It may be the house in which the Head of Household and his/her family lives, the businesses the Head of Household owns, or even the entire neighborhood (if the entire neighborhood belongs to the Head of Household).

Property Caretaker: The property caretaker is the Sim that takes care of or is in charge of the property when the Head of Household dies and the heir is too young to assume the heirship.

I think this would be interesting to add to a Royal Kingdom Challenge

I'm going to build this into my revised Test of Time rules for when I get to the Age of Empires stage. :D

Peni, I always love your gameplay posts -- you think of so many cool and creative ideas!