I think part of the reason why attack style ads don't work is because you usually need to choose some "villain", which just isn't feasable with more than 2 parties since voters will still have other options than you. Well, unless you vilify every party except your own but that kinda makes your party look crazy.

The closest I can think of is somewhat vilifying the extreme ends of the political spectrum since most parties can agree on that (assuming you have more than like 5 parties).