From the Super Mario Wiki
An Arachno Snifit is a large, black and red-legged type of spider which, judging from its similar facial features to them as well as the similar name, is a type of Snifit.
In The Super Mario Bros. Super Show! episode "Count Koopula", Mario, Luigi, Toad and Princess Toadstool, after jumping down a laundry chute and being deposited in Count Koopula's basement, find themselves menaced by several Arachno Snifits. Before these Arachno Snifits can attack, Princess Toadstool manages to scare them away using a fireball-spitting Magic Piranha Plant; after being hit by a fireball spat by this Magic Piranha Plant, an Arachno Snifit explodes in a manner similar to a balloon.
Any other Arachno Snifits inhabiting the castle were presumably crushed when it collapsed after Count Koopula's defeat.
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