One of the most shocking is when a tenant found out that the apartment they were leasing was actually being foreclosed on. They had paid months of rent in advance and then suddenly had to move out with no warning. Another shocker is when the landlord changed the locks on the tenant while they were out, claiming they hadn't paid rent when they actually had proof of payment.
A really shocking leasing horror story is when a tenant was living in an apartment and the building caught fire due to faulty electrical wiring. The landlord had known about the wiring issues but didn't fix them to save money. Thankfully, the tenant survived, but they lost all their possessions. Another is when a landlord used the tenant's security deposit to pay off their own personal debts instead of for any legitimate reasons related to the property.