Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
For example: An Ice type Pokemon would lose a little bit of HP each turn during Sunny Day to simulate melting, or maybe if something that was Stun Spore'd and then gets hit with a water move it loses paralysis to simulate washing off the pollen, or how about if something gets hit with a water...