I have a Epiphone Les Paul Custom Pro and today it was in a room where the door was open, and it was raining really hard (I don't know how the door opened). My guitar now feels a little slippery and I was wondering if somehow it could've been damaged. The door was open for a while.
Nothing major most likely. Open it up and check that there isn't any lingering water reservoirs or droplets.

If there is, sap it (them) up with toilet paper or something.
Schecter Hellraiser Solo-6 FR Limited
Parker Mojo Fly
Ibanez SZR 720
Tanglewood Evolution
LaPatrie Etude DEMO
'66 Hagstrom Viking I (customized)
SGR C-7 (defretted)
Agile Intrepid 828

Amp, Pedals:
Laney LV300