That move is fine, but Jibba is out of claw reach.
Round 376
Jibba misses with bite and tail (best missing roll 38), but wing buffets twice (rolled 43 and natural 20; 27 for failed crit) for 22 points of damage. Livox has 167 HP remaining.
As Jibba plummets into the water, Livox's tail AoO connects (rolled 39-7=32) for 28 points of damage. Jibba has 155 HP remaining.
Jibba takes 2 points of non-lethal damage from his fall into the water, and sinks 30 feet, unless he gets a swim check as a free action to stay afloat, in which case he does stay afloat (unless he does not want to do so). What have we been doing regarding this, and also, does a flying creature get to use its flying speed as a base when computing swim speed?