ref chilepepper
@the BAM
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Nothing in this arena blocks LoS so there in no way to hide unless your familiar can "hide in plain sight," is invisible, or somehow gets cover or concealment.

SRD-
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You need cover or concealment in order to attempt a Hide check. Total cover or total concealment usually (but not always; see Special, below) obviates the need for a Hide check, since nothing can see you anyway.


If your familiar stays behind, post out of spoilers for your opponent what square it's in. If it hides (and can fit) in a pocket, total concealment means auto success on the hide check.