edit: some language needed to be changed.
1. To use the tier 2 talents you need 3x level 20 pets or level 25 pets, preferably.
Your AH may not have cheap level 10 or level 25 zandalari pets., you also need to have a level 25 pet already, to use purchased level 25 pets, a previous level 10 to buy level 10 pets, etc. if you buy a level 25 pet, you can't learn/equip it until you've levelled a pet to the same level.
2. Fabled pets, hit like trucks, about 400-800hp. A lvl 15 should survive 1 hit, most times, it will be dead in 1 shot.
the zandalari's need to be able to survive 4 rounds to do much damage, at 20+ it's easier.
2. To get pokebuddy to work, you need to have done the first 5-6 battle pet quests (to get revive pet in your pet journal), and levelled a pet to level 5 to unlock 3 pet slots.
revive pets is the skill required to use PB, and you should get this ability after defeating the 3rd trainer in combat (level 6-8 pets needed)
2a. The quests are account shared, so any alt will do, and you will need to level the first few pets you have, to level 6 which doesn't take long to do by hand.
2b. You don't have to complete all 6-8 trainer quests. Doing so, unlocks the dailies, which will be necessary later to get access to the fabled pet quests, the first few are simple enough, the level 7-9-11 trainers will require battling other pets to gain XP, which will give you some familiarity with the system.
2c. or you can use PokeBuddy to level your first few pets in starter zones after level 6. your choice.
3. Completing any battle where your highest level pet is within 5 levels of the enemy, gets you player XP,
i.e. a level 14 in a level 10 area, or a group of level 23-25's in a level 19 area (northrend/outland).
completing 30-40 battles (about 12-15 battles/ hour), will give you a full level, and take a few hours. Pretty safe xp as well, since you don't have to move too far.
4. there are plenty of other farming areas to use if your pets aren't 20+ yet. look for "battle stone farming areas" on wowhead / mmo champ / forums for level 8/12/16/19/23/25 pets iirc, that swarm a location, requiring no player movement,
just combat bot and a few good ringer pets to heal through, i.e. crab/dragonkin/spider/frog. etc that can self-heal.
6. Poke buddy, by default, swaps pets when they get to 30% health. It can get messy with multiple swaps, as it will suicide swap as all 3 pets become too low
there's not much you can do except modify the logic and remove the health swapout "only" for level 25 pets, then save the edited level 25 pet logic to keep those settings around they will fight until they die, which works for most people.
7. for advanced pet collectors, (and if you have too many pets), you can use the plugins
Battle Pet Collector, which has a collection of GatherBuddy 2 paths to farm for pets across an entire continent, for the zookeeper achievement & title, "Zookeeper <name>".
Battle Pet Swapper, which will swap your current pet for a low level pet.
do not use BPC/BPS lightly, they're great, but the paths are predictable, and you can get stuck if you don't fully understand how the plugins work.
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if you have level 1 pets, and already have level 25 pets, this will help "boost" the levelling process very efficiently, (without gaining player XP)
1. Start levelling the dinos in a main city against lvl 1 pets, until level 4/5. use leap/bite or 2/1/1/1/1/3
2. at level 5, change to a level 12 pet area (level 40 mobs in feralas, hinterlands) or if you have bandages, a level 18 pet area, zuldrak has the waveling pools (easy to level from 15-20)
3. you can level using 2x 25's and a level 5-10 pet, swap the level 5 for one turn or let them get hit once, then swap out.
4. if in a rush, for alliance, go from wetlands to duskwood / stranglethorn / twilight highlands, or moonglade / winterpsring / hyjal (horde) to get those pets to 20 quickly.
alternatively, if you only have low-level pets (level 1-10),
5. do the starter and tamer questlines as you'll need to get 3 pets to 25, having some bandages will help with this.
it will take roughly 7-8 hours to get around the continents and complete the EK tamers, then kalimdor, then Outland, then Northrend.
(thank god it only really needs to be done once.)
6. this can be automated if you use pokebuddy and combat bot to fight pets and mobs along the way (be careful about setting the pet level differences on the first tab in pokebuddy)
level your 5's to 15 to survive 1 hit from a level 25 pet, they should get 300-500xp (or more) each win, winning 10 rounds against pets 10+ levels higher than yours, will usually bring a level 5 to level 12 quickly.
from level 12-20, stick with northrend and
cataclysm areas, hyjal, uldum, twilight highlands are good areas to slowly farm from level 13-18 using combat bot, move to jade forest/4 winds for level 17-24
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For a brand new account, no Level 25 pets.
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For a brand new account, your character level will need to be higher than 25 to get started, due to the trainers being in level 20 areas,
Use the quest line in the main city, start at level 20+, farm your pets to level 6 in the city (rested XP,), or in the starter zones, level 1-5 and 10-20 pets.
if you've never collected any pets, aim for ironforge's entrance to gnomeregan, the fluxfire feline can kill pets 5 levels higher than yours, little black ram is also good, but hard to farm.
as horde, undead starter zone has the lord of lordaeron, move to azshara (north of orgrimmar) for a crab (good tanking pet) along the shoreline (take the goblin rail to the last stop near the waterline). other specialty pets can be purchased (check the level first)
get your character to level 35 to get into booty bay for alliance or southern barrens for horde to fight area mobs and level 12 pets.
at level 12 pets, continue with the quest line, and unlock the EK/Kalimdor dailies (provides more pet XP than farming), staying 2 levels above the trainer if you can to save time.
unlocking the EK/Kalimdor trainers allows you to heal pets using the stable masters.
if you complete the EK/Kalimdor/Outland/Northrend/Pandaren trainers, you can collect a 3000g prize (1x per account)
make sure to farm pets specifically for Aki, it's not an easy battle to win for that 3000g, a good Beast / Humanoid / Flying pet.
specifically the flayer youngling/Kun-Lai Runt/corefire imp/ anubisath idol / Curious Wolvar Pup
effervescent glowfly, strand crawler, fel flame, shrine fly, wildhammer Gryphon Hatchling , etc. or zandalari anklebiter pets are good beast pets too.
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To defeat alliance trainers, you will need rare pets of the following type:
Mechanical, Beast, Elemental, Magic, Dragonkin, Undead.
To defeat horde trainers, you will probably need rare pets of the following type:
Mechanical, Beast, Flying, Magic, Aquatic, Elemental
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Once you've done the tamers quest line, you will have 3+ level 10 pets, and unlocked the continent dailies, as well as trainer healing and probably got some first pet bandages along the way from defeating the trainers.