Rather than dress like Mario the way everyone else dresses like Mario - with overalls and a red cap - these guys tried a little harder, building a propeller cap and, more impressively, the FLUDD from Mario Sunshine.
You can find details on how they were made here and here, which also double as a handy guide if you want to do something like this yourself. Should, you know. Volcanic ash prevent more conventional means of air travel. Or the streets get dirty and you have a fear of regular hoses.
While the FLUDD looks complex and slightly expensive, it apparently cost less than $40, so cosplayers on a budget are being well catered-for.