Marius will buy an artisan's outfit, assuming one that would be functional while adventuring can be found.

Spoiler: OoC
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Marius can afford it if the outfit costs 1gp. If it costs more than that, he may need a loan from Zauberei to cover the cost.

Marius' plan will be to change into the artisan's outfit for the descent/water pit obstacle and then change back into his explorer's outfit once he's on dry land again.