I need help to make THE WORST Landlord in Sims 4

If you have Realm of Magic, consider making them a spellcaster. If you're controlling them, you can have them use spells to break stuff, forcing them to pay you to fix things. Whenever there's a tenant revolt, they can freeze the rebellion in place.

If you don't want to play them and have Get Together, you can make a club of only them, and have one of their rules be to use bad magic. The other rules can be them being rude to your sims or even attacking them.