world of warcraft
All over WoW you can battle various wild pets and you can potentially capture them. They have all different levels depending on where you're battling them (higher level zones tend to have higher level pets).
For the Tournament of Celestials, you need to have 15 pets levelled to 25, that you "levelled yourself".
What counts as levelling them myself? Taking them from 1-25? Or can I encounter a level, say, 23 pet in the wild, level it 2 more levels, and that's countable?
You need 8 guild members in the raid for all pre-cataclysm raid achievements in 10, 20, and 25 man zones. 40 man raids require 10 guild members. 5 man dungeon achievements require 4.
And, with the exception of Naxx 40, yes, all of the old 40 man zones (MC, BWL, and AQ40) are still in the game.
Above is the action bar during pet battles. Each pet is able to use up to three attacks/abilities, these are buttons one to three. Button four allows you to swap your current pet for another and button five allows you to trap the current wild pet you are fighting. The last option is Forfeit that allows you to flee the current battle to fight another day!
Once you have trained the ability to battle with pets, you are able to track creatures that can be captured using 'Track Pets' on your mini map:
To start a pet battle, simply find a suitable wild pet and right click on them to begin a pet battle.
In order to attempt to capture a pet you must fight until your target pet is below 35% health. This will enable the capture button. You potentially could accidentally defeat the pet by continuing to attack below 35% rather than using the 'Capture' button.
Using the capture button will allow you to attempt to capture the wild pet. It is not a guaranteed capture, but at lower levels it is generally successful.
Best Answer
In order for a pet to count as being "leveled yourself", you have to level it up at least one time. You can buy level 24 pets, level them up once, and this will count towards the 15 pet requirement.
This is confirmed in wowhead comments for the Pro Pet Group achievement.