Guide to evolving a pet

Death leveling pets is the simplest way to obtain a fully evolved level 20 pet. With the right setup, it can be completed in 15–20 minutes. This method will result in a hearty pet, which will allow you to unlock all evolutions at the Zaishen Menagerie.

Details
Death leveling can be performed "in the wild," as long as you clear out all nearby enemies before doing so. However, it is much easier to charm an animal, release it into the Zaishen Menagerie Grounds, and perform the death leveling there.

The quickest method requires two heroes, a mesmer and a necromancer. The following builds should be used:

Your build
N/R or R/N will work.

Equipment:
 * 5 superior runes to bring your health down to 105.
 * Optional: The -50 HP Grim Cesta to bring your health down to 55. Not absolutely necessary, but it makes the process quicker.
 * Any vampiric one-handed weapon (sword, axe, spear).
 * Optional: Any +Health weapon to help keep you alive after you've accrued some death penalty.

Mesmer hero
Equipment doesn't really matter, but Radiant insignia, Runes of Attunement, and weapons with +Energy are recommended.

Necromancer hero
Disable Succor and Mending so that he will maintain them. Have him cast Succor on the mesmer hero and Mending on himself.

Again, equipment doesn't really matter, but a weapon of Enchanting is recommended.

Walkthrough
Travel to the Zaishen Menagerie Grounds and find the animal you want to death level. Aggro the animal either by attacking or by activating Charm Animal and then canceling it. Any animals of the same species will also aggro when you do this; you should kill off all but one of the animals, otherwise they will share the experience from your deaths, reducing the rate at which they gain levels. The animal will not attack, but will continue wandering around randomly, meaning it may wander out of your aggro bubble and out of range to gain experience from your deaths. Unless you are watching the process and can move your character to follow the animal, this can lengthen the time required substantially, depending on how far the animal wanders.

Switch to the vampiric weapon, then kill yourself by casting Blood is Power on either hero. If you had 55 health, the -15% Death Penalty will reduce your maximum health to 1. If you did not have 55 health, let yourself be resurrected by RChant or Vengeance by immediately switching off of the vampiric weapon, wait a few seconds for the non-Death Penalty delay to expire, then kill yourself again; repeat until you have a maximum health of 1.

Your mesmer's Restore Life and Resurrect skills will now bring you to life with less than 50% health, i.e. 0, meaning you die instantly. Resurrection Chant and Vengeance will leave you at 1 health, but the vampiric weapon will drain that in less than a second. On average, you will die 20 times per minute. With 338 deaths required to level a pet from 5 to 20, it will take a little over 15 minutes to obtain a dire level 20 pet.

When the animal has reached level 20, have the mesmer hero use Resurrection Chant, then immediately switch off of the vampiric weapon. Charm the animal, then return to Emryd the Tamer to register it.

Getting a dire pet
If you want a dire pet, you can use the above method to evolve a hearty pet, register it with Emryd to unlock both hearty and dire evolutions, then have Wynn summon the dire version for you to charm.