You should have probably asked or checked for this in the Ness Q&A first.
It is impossible to get out of it at some percents with some characters, but DI up and towards Ness can get you too high to be Fair combo'd with alot of characters. Although, sometimes the Ness can mix up the combos with Up Air instead of Fair.
With some characters or at high percents, you can DI away and down in order to be too far to get combo'd anymore. This is probably the best choice if you can do it.
Try your best to not get grabbed by Ness in general, as that is how he gets alot of his damage and kills in.
