I hate to say that a lack of Castaway is not a great idea when running Mario. The best thing you can replace it with is probably draw, but you NEED those tools. You might have to tech a Ledian if you can't find any other way to get cess crystals, but that is highly unrecommended.
its not a very good idea to add in starters for a mario deck since it slows the deck down, but you might want to think about using a mawile to search for trainers and tools.
Umbreon has a point. Mario is not as efficient unless you have those Castaways. If you're playing for fun, cool, but if you want to get some wins, you really need those castaways. Slow Mario is an unfriendly mario.
You need at least 2.
Otherwise, replace it for more PP/Strength Charm/Buffer Piece/or CC.
Quick Ball works fairly well too for speed if that dosn't work out.