Attack Pattern: They bob upwards in the water as they chase after Mario, and stop to float slowly downward when they get tired or rise too high in the water. They follow Mario around the screen and their bobbing motion makes them a bit difficult to predict. In the Lost Levels, some can fly in the air using the same attack pattern.
Basic Fighting Strategies: You can't stomp them under water, so your best bet is to avoid these nuisances. Once you get past them they will not be able to keep up with you. Fireballs are very handy, if you have them. Advanced Strategies: Again, use fireballs if you have them. In the Lost Levels, you can earn a respectable 1000 points by stomping on the ones that float in the air, but it may be more trouble than it is worth.

Attack Pattern: They follow a pretty similar attack pattern to Super Mario Bros, bobbing up and down, and slowly floating towards the ocean floor when they get tired. Some have a trail of babies which will follow them around, making them a bit harder to avoid, and some can even cause the babies to swim out in all directions, like projectiles. I think they swim out at predictable angles, so just try to swim between the babies.
Basic Fighting Strategies: Stay away from them! Hammers and fireballs will kill them if you have those power-ups, and invincibility should work too, although it is only a temporary solution. It is usually pretty easy to keep your distance from the Bloopers in this game.
Advanced Strategies: Try saving any fire flowers that you get at Toad Houses and other places for the swimming stages of this game. They make these levels much easier, and may even be better than frog suits in some cases.

Attack Pattern: On the map, they act much like the Bloopers in previous games, bobbing upwards and then slowly floating back down to the sea floor. Some have babies, and each baby fights as if it were an adult Blooper. In battle, they use regular attacks and they will also blast characters with a powerful cloud of ink, which can cause a lot of damage. They are prone to running away from battle.
Basic Fighting Strategies: You should probably attack Bloopers about halfway through the battle, because they aren't too dangerous, but they're easier to beat than some other enemies they appear with and they will sometimes make you Lucky in battle. Lightning, Geno Beam and Fire attacks all work very well. Most other special attacks are not very good. You may be able to beat them with one timed-hit if you have a character with very high offensive power.
Advanced Strategies: Blooper will run away from you if you use a regular attack on it and it survives, so it is best to use special attacks. Mallow's lightning attack will normally kill all Bloopers on-screen with one hit! Contrary to what the official guide says, you don't have to use a Yoshi Cookie to get Lucky from Bloopers.
Blooper's regular attack is a bit weird. It dives down below the ocean floor and pops back up in front of the chosen target, then punches that character with its tentacles. Try to press A just as the punch connects with the character to block.

Attack Pattern: Blooper will ambush you in the sewers below Toad Town. It uses ink attacks and has smaller Bloopers to protect it.
Basic Fighting Strategies: You can't use ground attacks since Blooper floats in the air. Use jumps.
Advanced Strategies: Don't go too far into the sewers without saving as there are multiple Bloopers down there and they are fairly tough.

Attack Pattern: Bloopers hang around Ricco Harbour. They move pretty slowly, but they can spit goo which will spawn those tiny jelly-like enemies when there is a lot of it. If you get close to them, they will try to whip you with their tentacles. They can hang from the bottom or crawl on the top of catwalks. Beware of Bloopers hiding on the bottom of a catwalk, they may pop up and surprise you as you're running on the top!
Basic Fighting Strategies: You can stun Bloopers and knock them off of catwalks by using FLUDD, but to kill them you must jump on them or dive at them by running and pressing B.
Advanced Strategies: Listen for the sound of their tentacles to tell when one is nearby: this can save you from a surprise when one is hiding underneath a catwalk. It's best to use a butt-stomp to kill them, you'll get a coin and it's easy to do without falling off the catwalks.