To find Gavial the player must have spoken to the "Huntmaster" in Phon Coast and defeated Thalassinon, which will trigger the start of the Rare Game quest.
The player must close the no. 10 sluice gate and enter the area drained of water. Gavial is not found on one of the upper walkways, but down in the channel. After waiting 10 to 15 seconds, Gavial will come running towards the party.