I had a request to post the rules on LJ as well as on Boolprop, and I'm a very accommodating person, so here they are!
So I had an idea for a challenge, and I thought "Hey! Maybe other people would be interested too!" I don't think there's another one like this out there. Let me know if anything is unclear or unworkable, and I'll make modifications as needed. Please note: I haven't playtested this yet. If someone wants to beat me to it, I'd welcome any feedback.
THE CRAZY CAT LOVER CHALLENGE
The concept is simple: your Sim is the type of Sim who would have once been referred to as a "crazy cat lady," but that's such an incorrect term nowadays: men can be just as nutty about cats if they want to.
Setup
Pets is required for this challenge.
This is a single-generation challenge: when your starting sim dies, the challenge is over. If you want to continue with your starting Sim's child, you have to start over from zero.
Take a single Sim and move them into any house they can afford. This Sim can be a CAS Sim, an EAxis premade, or one of your own playables that you find rather boring. You get no points for anything pertaining to the actual Sim, so there are no advantages to starting with a Sim who has friends or skill points.
The Rules
1. Cats must always outnumber Sims by at least two-to-one. This means that the maximum number of Sims you can have on a lot is three. (3 sims x 2 cats per Sim = 6 cats, and 3 Sims + 6 cats = almost at the lot limit.) You can have a higher cat-to-Sim ratio, but it can't go lower.
1a. If your Sim gets married and has twins, too bad. You have to put one of the kids up for adoption. (I recommend moving in another adult Sim and moving them out again immediately with the superfluous child.) Alternatively, your Sim could divorce their spouse.
1b. If you have a hack that raises the lot limit, you don't have to give up any children, as long as you keep the ratio at 2 cats for every Sim. However, if you ever have to choose between a child and a cat, choose the cat.
2. You must have your two cats before the Welcome Wagon arrives on the day you move into the house. You can make the cats in CAS with your Sim, make them in CAS and them move them in, buy them at a store, use the pet service, adopt strays -- whatever you like, as long as you're done before the Welcome Wagon arrives.
3. The cats are the most important things on the lot. If a cat wants to interact with a Sim, the Sim must stop what they're doing to enable the interaction.
3a. If multiple cats have interactions lined up, it's first come, first served. Never cancel an interaction involving a cat.
3b. If the interaction in question is "Pounce," you do not have to cancel what your Sim is doing -- the cat will complete that interaction regardless.
3c. If your sim is engaged in a non-autonomous action with a cat (that is, something that you told the sim to do) and a different cat autonomously decides to interact with your sim, you must cancel the non-autonomous action to allow the autonomous one. (The cat may very well wander off before the action cancels, of course, because cats are like that.) This does not apply to "Pounce;" see Rule #3b.
4. Your Sim can never have a job, but the cats can have as many jobs as you would like.
4a. Any form of at-home income -- novels, digging for treasure, painting, stock tips, etc. -- is allowed, as long as the Sim stops what they're doing when a cat wants to interact with them.
4b. You aren't allowed to earn any career rewards, but if your Sim is a playable who inherited something from Grandma before the start of the challenge, it's okay to use it. This inheritance is limited to one career reward, though. Grandma had other people to leave stuff to.
5. Elixir of Life and Kibble of Life are not allowed. (You get points per cat, so you want to make room for more. Besides, if you can go forever, where's the challenge?)
5a. All aspiration rewards other than Elixir and Kibble are allowed.
6. Your Sim may not shoo a cat off of a piece of furniture they want to use. They can always sleep on the floor, as long as the cat's comfortable.
7. Your Sim may not take a vacation. (Nobody else would take proper care of the kitties.)
8. Trips to community lots are limited to three hours or fewer. (Are the kitties all right without me?) Phone calls, internet chat, and inviting people over are all just fine, as long as Rule #3 is followed.
9. Keep all pet graves on the lot. (Any Sim graves can go to a community lot if you like.)
10. You may not give away any cats. Your Sim would give up their own child first -- literally, if Rule 1a applies.
11. If the cats get taken away by the pet services agency, the game is over. Otherwise, the game ends when your Sim dies.
11a. If your Sim dies with no other Sims on the lot, the cats will be taken away by pet services. This is supposed to happen and does not incur a penalty.
12. You may Praise or Scold a cat as much as you like, since it doesn't affect your score.
Points
Plus points
+1 Each command learned (except Use Toilet; see below) This stacks: if Mr. Fuzzypants learns Roll Over and Come Here, and Queen Snuffles learns Come Here and Shake, you get 4 points.
+5 Each career topped by a cat (This also stacks -- if Mr. Fuzzypants and Queen Snuffles each top Service, you get 10 points.)
+5 Each kitten born on the lot
+9 Individual portrait of each cat somewhere on the lot (painting, snapshot, artist's camera, architect's table, etc.)
+9 Each cat has its own "stuff" (bed, food bowl, litterbox, scratching post, toy mousie, and bird-on-a-stick; a cat condo counts as a combined bed/scratching post)
+10 Each stray adopted
Minus points
-1 Each fight between your Sim's cats (Fights between your Sim's cats and any walkbys/strays don't count.)
-5 Each time a cat older than kitten used the floor instead of the litterbox
-5 Each item of furniture destroyed
-5 If you the player can't tell the adult cats apart (All kittens look alike, so they don't count)
-10 Playing with a dog or puppy that walks by
-15 Becoming a werewolf (Why was your Sim neglecting the kitties?)
-15 Each cat that runs away
-50 If cats are removed (If the reason the cats are removed is that the last Sim on the lot dies, there is no penalty)
Bonus points
+1 Each friend that each cat has at the end of the challenge (This stacks: if Mr. Fuzzypants has 5 friends and Queen Snuffles has 7, you get 12 points)
+2 Each cat that considers your Sim "Mine" at the end of the challenge
+5 Each cat that learns Use Toilet
+10 Each cat that has special content unlocked over the course of your challenge (for example, Neon Pink Fur) Special content is unlocked by topping pet careers.
+20 If all cats on the lot at the end of the challenge have topped all careers
+20 Having as much cat-themed decor as you can fit in the house/stand to look at without throwing up Revised on 3/16/13; see below.
+50 If both starting cats are strays adopted before the Welcome Wagon arrives
+50 If all cats on the lot at the end of the challenge know all commands
+50 If you start with twenty kittens at the same time and raise them all to full-grown cats simultaneously. (This will require a larger households hack.)
Decor bonuses
+1 for every different cat-themed item used from Build mode. (For instance, there are three wallpapers with cats across the top: red, yellow, and blue. If you use each color, you get +1 per color used. If you use the yellow version in two different rooms, you only get 1 point.)
+1 for every different cat-themed item used from Buy mode. (For instance, there is one Lucky Cat statue, but it comes in three colors: black, white, and gold. +1 for using the statue, no matter how many times you use it or what colors you use.)
........Exception: If you use no cc at all, then +1 for every recolor you use. (For instance, if you use no cc at all, and.place one black Lucky Cat, one white Lucky Cat, and one gold Lucky Cat, you get 3 points. However, if you place a second white Lucky Cat, you don't get any extra points.)
+1 for using a cat-themed item from every sub-category within a particular Build/Buy category. (For instance, if you added a cat-themed toilet and a cat-themed sink and a cat-themed shower and a cat-themed hot tub, you could take this point, since there is one object for every sub-category under "Plumbing.")
+1 for every category in which Sim has cat-themed clothing (Everyday, Pajamas, etc.)
+1 for having cat-themed accessories (whether categorized as glasses, as Bon Voyage jewelry, or both)
Cheats
Cheats or hacks that save clicks or make purely cosmetic changes are allowed. (So all building cheats, moveobjects, any cheat that lets you place things where they wouldn't otherwise be allowed to go -- all fine.)
Cheats or hacks that make the game easier are not allowed. (So money cheats, motive cheats, anything that lets you control the cats -- all banned.)
And that's it! Let me know what you think. (Especially about the points -- I had trouble with that.)
Update history
2/15/12: Added Rule #1b in response to a question from playtester SuperFrog
4/8/12: Added "toy mousie" to the list of "stuff" each cat should have -- how could I have forgotten?
4/24/12: Added Rule #11a and clarification to the "Minus Points" section in response to a question from Lorinsv and information from joandsarah77
4/27/12: Added Rule #12 in response to a question from joandsarah77
6/9/12: Added an opportunity for bonus points in response to a discussion between Pony and animeangel1983
3/16/13: Completely revised the scoring for cat-themed decor based on discussion with reader and playtester Lorinsv60. About 98% of the way the new scoring works is hers, but I take credit for the clothing points. :)
12/25/13: Clarified that a cat condo can count as a combined bed and scratching post.
1/20/15: Clarified what to do if you have a non-autonomous action lined up with one cat and an autonomous action from another cat shows up in the queue.