Just go to the Eterna Forest at night.
Chat with our AI personalities
You can catch a Misdreavus on Mt. Silver, The Cliff Cave, or the Safari Zone (has special requirements).
Misdreavus must be traded from DP, HG or SS as it is not found in Platinum.
trade from leafgreen
In the cliff cave in cianwood city
You can't catch it in Emerald, sorry. You have to trade one from Pokemon Leafgreen.