Another way to make the game harder is not to fill any wants or to do anything in to raise mood, or fill any part of an aspiration. They go into aspiration failure. To remove all comforts, and electronics, and other things. Maybe try locking a few in an empty room. No windows because they gain comfort from auto looking out windows. You can do this with one Sim in one room locked if you want to continue playing the rest of them. Aspiration failure is probably the most fun thing to do in TS2 for deviant play. Otherwise it can be as hard or easy as you want the game to be, because Sims care about room sizes, light from windows, and types of windows, wallpaper and floors (expensive makes them happier) but they can also be very happy in small rooms, decorated so it's really all up to you if you baby and coddle them or not.
Those outgoing Sims need socialization, why not take some of that away? No mods necessary.
Active Sims need more food. Hunger is a good motivator.
Neat Sims will clean and be very happy, why not take away that fun by not letting them clean anything.
If they have nothing to do they play Kicky Bag, if no one is the room, they can't play it. :D
If they are bored and or need social or fun, they relax on beds to fill those things...no bed..no fun, no comfort, no sleep.
Art and decorations are fun for TS2 Sims, zero objects to look at equals no fun.
Chance cards can demote or get Sims fired..try a few.
Cheating Sims can ruin lives and relationships for weeks. Don't let anyone apologize or try to rebuild the relationship if you enjoy fights.
Grumpy Sims are mean to other Sims, sometimes they cause fights.
Popular Sims want more friends why not cause some of them to lose friendships (this is not that possible anymore after BF or BFFs) It won't work.
Why not fill some fears..those are fun.
No money equals the repo man coming to take things away. Don't pay the bills, and don't let Sims auto pay them.
Burning food is a good gossip topic. Let Sims cook harder foods under 'Make' instead of Serve, to see if they can start fires or burn food..with zero skills. Have them make something they never have learned to cook.
Objects in TS2 equals happier Sims..such as a cheap stove can only fill the hunger to 4...a nice stove fills hunger faster, and for longer because it has 10 points, cheap stuff makes them hungry sooner, or need more rest in cheap beds, have to sleep longer and have to sit more often due to lack of comfort. Take away the nicer furniture and appliances with higher points, because all those work faster and last longer for the Sim's mood.
They are dozens of ways to make the game harder for your Sim.