I am a landlord who bought a rental property with a tenant who has a pet deposit in their lease. The named LL in the lease is the prior owner. The tenant has vacated before their lease expiration date and I have damages and lost rent. Is the deposit legal, and if yes can it be used to mitigate damages and lost rent? Thanks.

There is a link in a "sticky" at the top of this forum to each state's LL/tenant laws. You should be able to find the answer there and/or in your lease. By purchasing the property you purchased the lease and everything contained within it. Most leases contain wording about what the deposits can be used towards.