If there was water already underneath them, yes, they couldn't use Nagashi. But the timeframe would look like..Oh, I almost forgot about that XD
I focus my chakra and forcebly insert it into the opponents chakra system and manipulates his senses, trapping him in an illusion. In the illusion, I suddenly dissapear from sight, and bean vines rise from the ground all around him. They lift him up into the air and a bean pod rises drom the ground underneath them which I come out of, and dash, with a sword ready to strike. Outside the illusion, Im arcing towards him and slash his neck off
Well, this is one of the few normal genjutsu that paralyze an opponent. So of course you have to attack. I wouldnt try to get in close though, as theyd more than likely use nagashi and break from the illusion and stop my attack with the same jutsu. Earth Jutsu is pretty much useless because of this. So, Id use ( Katon: Gōka Honoo no Hashira Jutsu ) - Fire Release: Great Fire Flame Pillars Technique or you could use (Suiton: Suiryū Kōbaku ) - Water Release: Water Dragon Biting Explosion also meaning they couldnt use nagashi, so there options would be evn more limited, so most likely they would use Added rock weight, but that would work against them.
( Katon: Gōka Honoo no Hashira Jutsu ) - Fire Release: Great Fire Flame Pillars Technique
Rank: A
Type: Offensive
Range: Short – Mid
Chakra cost: 30
Damage points: 60
Description: The user will knead their fire chakra and release it into the ground by stomping down their leg and then causing three pillars of fire several meters tall spaced out evenly. The Pillars of fire can act as a defensive wall against incoming techniques or targets or used to attack low aerial targets.
(Suiton: Suiryū Kōbaku ) - Water Release: Water Dragon Biting Explosion
Rank: A
Type: Offensive
Range: Short - Long
Chakra cost: 30
Damage points: 60
Description: The user creates a large pool of water that gushes upwards lifting the opponent into the air, after firing the enemy into the air, the user shoots numerous water bullets at them from the pool of water and then finishes by forming the water bullets into a water dragon which attacks the target, sending them crashing into the ground.
(Insert Genjutsu)
Nagashi
Water Biting
So unless you had a clone or a partner to perform the water technique at the same time, I would say he could manage nagashi without shocking himself