Nemesis is your long-stand rival in the game. Just like Harry Potter's foe Voldemort, he/she can be evil as a demon. This relationship status can only be attained once you've reached "Sworn Enemy" status with another Sim and it should be at least Level 8. Intensifying this kind of mean relationship will leads you to become Arch Nemesis, the meanest of all means.
Generous These Sims give a bit better daily Login Rewards
Lucky These Sims occasionally give you bonus XP while at home
Mean These Sims get a bonus every now and then when being insulting with others
Competitive These Sims are a bit better at Rival Events
Good Upbringing These Sims are way better at all Events