Event Match 18: Link's Adventure is an Event Match availible in the Event Mode from SSBM.
This is simply defeating Dark Link, who is the same as Link except for the fact that he's dark.
The title of this Event Match most likely is a refence to Zelda II: Adventure of Link, which featured a final battle against Dark Link, as well.
Strategy
Try to chain grab, then throw up, then Uair until the opponent is at about 150%. Use Dair and the impact sends him flying. Be careful as Shadow Link will return with his second stock. Just shuffle or wave dash to avoid any serious attacks.