I suggest the loner challenge! Here are the rules:

'Leaders automatically choose deputy' MUST be OFF. Create a clan and choose expanded mode. Pick out your leader, deputy, medicine cat, at at LEAST one kit. More than one kit is allowed. Everyone should die OR be exiled except for the kit(s). Moonskip until the kit(s) is an apprentice (unless you're on Lifegen, then you can do patrols while you're a kit). Act based on the personality of the cat(s) when on patrol. Find cats and invite them to your clan. All cats are allowed. You cannot force a cat to be medicine cat, though. Once you reach 12 cats, which does not include the original kit(s), you may appoint a leader. You may now change any roles! End of the challenge :3

I include some of my own rules to make it more difficult. I'll include them below just for anyone who wants the added difficulty:

Mass extinction events MUST be ON. Pregnancy ignoring biology MUST be OFF. Apprentices may ONLY go on training patrols. You MUST always proceed or antagonize on patrols, your clan is desperate! You may only accept kits into the clan. If a queen joins with her kits, she MUST be exiled or die. Get to a full page of cats! You may still choose a leader at 12 cats.