Aquaria/Pets

There are four pets in the game, which are all gotten by beating a boss that guards them. Pets follow you around and help out in some way, usually by providing minor combat assistance. Pets will not attack most harmless creatures. They can also follow you anywhere, including through fish tunnels and strong currents. When traveling in Fish Form with a pet, they will draw enemy fire to themselves, and consequently you, even if normally the enemy would ignore your presence in this form.

Where to find them

 * Nautilus: Found south west of Naija's home, guarded by Nautilus Prime and its children. It attacks quickly and is likely the first pet you will get.
 * Piranha: Found in the very northeastern section of the Kelp Forest, which you can only get to with fish and beast forms. Defeat Mergog to obtain the egg. Piranha is slow to attack, but once it attacks an enemy, it latches on and rapidly bites three times. If it eats a shooting enemy, you will gain it's shots in Beast Form as if you ate it yourself. They can be summoned, swapped out, or put away on the pets menu, by clicking on their respective eggs.
 * Blaster Peg: Go back to the Energy Temple with the nature form and find the path to the square, previously unexplored chamber (can be approached from north or south). Go to the red flower near the path's north entrance and use nature form to get the pearl. Bring the pearl west and north to a previously locked door. Put the pearl in place, energize it, and enter the chamber, defeat Blaster Peg Prime and collect the Pet Blaster egg. It fires three homing blasts when it attacks.
 * Dumbo Octopus: In The Veil, near the sun temple, head right down to the bottom to a crack and use fish form to go through. Continue on through the small cave system past a bunch of enemies (you'll need Sun Form). Defeat it to get the pet egg. This glowing pet is handy if you want to use other forms from light in the dark, but pointless anywhere else as it does not attack.

Nautilus Prime
Use the energy form to shoot the spot not protected by its shell. Nautilus attacks slowly and for only small amounts of damage; however it has a dash attack which can catch you off guard, especially if you stumble upon it early in the game, so it is generally a good idea to keep moving around and to keep an eye on the small Nautiluses floating around.

Mergog Prime
Simply use your Nature Form, and plant cacti around the area where he rests. Planting cacti will also help shield you against his attacks.

Alternatively, in the bottom of his cave, just barely past where he appears on screen, there is a small section where the thorn vines dip down, just before the floor raises up. If you go into Energy Form and float there, his charge and energy attacks can't hit you, and yours will be able to track him as he moves about the cave. Just sit there and keep firing until he dies.

Blaster Peg Prime
First kill all the small Blaster Pegs, which do some damage if you're not careful. Then focus on the Peg Prime when there are no Blaster Pegs on screen. Keep moving around and you should be able to dodge all, or most, of his attacks.

Dumbo Octopus Prime
This is probably the easiest pet boss to beat, so long as you have the Urchin Costume equipped, which you really should by this late stage in the game.

The Octopus has several attacks, including tracking energy beams, grabbing you with its tentacle and slamming you around, spawning small octopuses, and squirting ink out to blacken the entire screen.

Crucially, its weak spot is only revealed when you get close to its mouth. If you position yourself at point-blank range to this location, you will be able to damage him without taking much damage yourself. In fact, you don't even need to see or move at all as the only things that can successfully attack you are the drone octopuses and the ink blind.

You will need a handful of healing items, but the damage is so slight that the simple +1 class items will do the trick.