Well it's not a standard field. It's that world's hell which manifests as individuals version of hell. If this could mess with the either of their heads, it could change the outcome. I can imagine Genie's hell as being permanently bound to the lamp.
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That was just Jafar using his superior magic to transform Genie into a temporary old version of himself, a spell/transformation/reality warp Genie got out of a second later. It was during the song "Your only second rate" iirc.
IMO Genie's hell would either be exactly after Genie!Jafar's imprisonment, and having Aladdin not set him free. That or it's during the battle, which ends with Jafar victorious.
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