H.A.R.P.O.O.N.

The Heavy Airship Rampaging in Practically every Ocean Or Nautical area is a blimp with 4000 HP. It may not seem much for a boss, but that's before you read the abilities. It moves at 95% the speed of a Z.O.M.G., and contains 2 Fishing Bloons. It is the boss of the special mission Something's Fishy. It was created with stolen parts: A spike factory and a Monkey Buccaneer harpoon. Strange, as the monkeys have quite high security. It would take someone with quite a lot of knowledge to get into their weapon storage...

Abilities

 * Chain Shield (Passive): Like I said, a boss with just 4000 HP? That's the health of a Z.O.M.G., maybe less! Well actually, a Z.O.M.G. is pretty tough... Anyways, the chain shield is what makes this boss a BOSS. It's freaking 5000 AD worth of Shielding! You can't break past that! Plus, it's always on! That's what makes the H.A.R.P.O.O.N. so tough. Fortunately, the shield is negated when it performs an attack. For 5 seconds. Plus, you can actually destroy the shield! 1000000HP. A lot. So go with the "Wait for an attack" strategy.
 * Fish Slap: Uses its fins to slap the 2 nearest towers. It does 7 damage. It has to take off it's chain shield to do this, so you can attack it while it's slapping. Again, the shield is negated with every attack.
 * Fish Summon: Ejects 5 Fish Bloons out of the Spike Factory top. They are ejected 75 pixels ahead.
 * Fishy Teeth: Impales a tower with its fishy teeth. The tower takes 5 damage, and there is a 50% chance of it to get the status effect Salmonella. If it bites an Inorganic Tower, it hurts itself and loses 25HP.
 * Fishing Help: Sends out a Fishing Bloon.
 * Catch of the Day: Sends out a Ceramic Rank up Non-blimp bloon. For some reason, only a 3/3 Fishing Monkey can catch it. Only uses it once. It seems to be covered in some sort of water.
 * Final OM NOM NOM: After down to 100 HP, it releases 50 Fish bloons, and eats 49 of them. It regains 490 HP.

Trivia
BGM right here.

This is the bloon that appeared at the end of Mining For Secrets.

It's less ugly than the F.E.A.R.