He is always found in the deep lake at the bottom of the level surrounded by a large shoal of ordinary Piranhas, and is very hard to defeat due to his high total of hit points and the fact that you need to fight him underwater, where your mobility is reduced.
Old Bitey drops a Golden Idol on death and is able to drop Crates as well, killing him will also allow you to collect the loot found on the lake bed in safety, including a number of Crates and a Coffin that contains the Viking Spelunker if not unlocked.
As with many bosses, killing Old Bitey unlocks a Deathmatch Arena.
Due to the high mobility and health of this monster, it is often best to try to lure him to the surface and throw Sticky Bombs at him from above, where he cannot retaliate, although finding an effective angle can be difficult. It takes four bombs in total to kill him.
You may wish to clear out a few of the smaller Piranhas before attacking Old Bitey, as they can often block your attacks. A Shotgun can be effective at thinning dense schools of Piranhas and damaging Old Bitey, but is also risky as you need to dive into the water to be able to target them in this way. Always try to give yourself a lot of room to prevent being mobbed from all directions, as this will usually result in you losing health very rapidly. As with many other mini-bosses, a Freeze Ray is also very effective against Old Bitey.
If you were fortunate enough to obtain a Shield from the Haunted Castle, it will work just as well on Old Bitey as it will on anything else, as he does not attempt to swim above or beneath you once you are shoving him with the shield. Be aware that doing this may destroy some of your loot in the process of crushing Old Bitey, and as ever, watch out for the smaller Piranhas coming up behind you.
- During the Daily Challenge Mode, the contents of the Crates dropped by Old Bitey will be different for all players, leaving the possibility for one player to get a Jetpack while the other gets a Parachute.