The Ranging Bloyster is a boss in Pikmin 2. It is a massive sea-slug creature that goes berserk when approached by Olimar or Louie. It can pivot around quickly to give chase to prey and has a ferocious appetite for Pikmin. In order to triumph over this enemy, you can use several methods, listed in order of effectiveness.
Quick Switch: This tactic requires both Olimar and Louie attacking the bloyster as single force. Whenever the player switches control of Olimar to Louie, the bloyster will pause for a moment in order to find its target, which is the active captain. You can tell because the red/blue glow will leave and then will return. When it is trying to find its target, it cannot move. In other words, as long as you keep switching control between the captains, you can sneak behind it and take it out without any trouble by tossing Pikmin at the bulb, likely without losing any Pikmin.
Dual Attack: This tactic requires both Olimar and Louie attacking the bloyster from opposite sides as separate groups. This maneuver requires plenty of space. The bloyster will charge your active captain, and while it does, switch to your other captain and advance towards the bulb. If it figures this out and attempts to find the real active captain, simply switch forces and attack once more, which should be easy, seeing as how the bloyster should have turned around by now and attacked where you once were. By repeating this strategy, the boss will die, but casualties may occur.
Last Resort: If you do not have both captains but have come to far in the dungeon to give up, this is your last resort. You'll have to attack directly with a full force. Stand in front of it for a split second and it will rear back to unleash the Pikmin-devouring tentacles. Right when it does this, you MUST run around to the back and toss frantically at the bulb, causing as much damage as you can before it swivels out of your reach. You can kill it in this way, but it is most unwise and costly, and it will drag out the battle. Ultra-Spicy Spray is beneficial here, but not foolproof.
"Arachnorbs boast a wondrous biological composition, with a silicon-based exoskeleton and innards coated with malleable heavy metals. However, much about these creatures remains a mystery, as specimens regularly explode when they are dissected. These explosions produce scorching flames that completely melt all internal organs, leaving us with a disappointing lack of information on the inner workings of the species. We must await the development of new dissection processes and more specialized research before we can better understand this enigmatic creature. However, the following observation notes have been recorded: appears to be leveling terrain for some unknown purpose... Location of eyes and ears not readily apparent... Freezing a specimen may yield new research opportunities."