Ness - PK Flash : )
Young Link. Depending on damage. if High, charge a downsmash or a fsmash (careful to miss the first hit and only hit the 2nd, I think that works lol) and of course dair if the opportunity is there. Down Tilt into something may be viable, not positive.
For more complicated measures, throw a boomerang far away. Pull a bomb. Jump and toss bomb down, boomer hits them, and you dair them. Timing is mega strict but it's... ****ing cool.
Link can probably do something like that too.
Bowser - Fsmash right?
Luigi... Up B? Or maybe light nair into something for damage?
Mewtwo... meh. Charge Shadow Ball. Probably better off using charged downsmash to hit though. Not positive. Why the **** would you be doing this matchup LOL
Game and Watch... You could always pray for a nine, but a charged up/forward smash is probably the way to go.