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So, yeah. Without a DM Fiat that says he gets +8 AC from water...He's dead...Sigh. So, being in water has the same protection as Full Plate? Well then, since he can only swim as far as half his base move. I Rapid Shot him again to make sure 'the blood in the water' isn't just blood coming out from the wounds he already has.

Attack 1: (1d20+9)[28]
Attack 2: (1d20+9)[18]

Damage 1: (1d8)[2]
Damage 2: (1d8)[8]
+4 to rolls if he's Human