Special thanks to Speane and Remington for formatting the thread.
Press Ctrl + F and type pet name to search for your pet quickly.
Pet levels:
If you get a pet for the first time it starts at level 1. Any dupes adds + 1 level up until their max. Some cap at level 1, while others go up to level 3 or even 5. This will be indicated with (#). Which explains the "per level" in the perk description.
You must "drop" pets to register you owning them for the first time, or else any duplicates will be added to your inventory and the only way to fix that is Ene manually editing your character file.
Examine: Right clicking examine on your pet in-game will provide you with a description of its perks as well.
Ikkle Hydra (1/1000)
Gives 5% additional accuracy and damage with Ranged attacks per level against your Slayer target. (3)
Gives 5% additional accuracy and damage with Melee attacks per level against your Slayer target. (3)
Gives 5% additional accuracy and damage with Magic attacks per level against your Slayer target. (3)
Gives 3% additional accuracy and damage per level against your Slayer target. (3)
Senty (1/1000)
There is a 10% chance per level that your Catacombs key will be saved upon use. (3)
Abyssal Orphan (1/1000)
Increases the Abyssal Sire's stun duration by 15 seconds per level (3)
Baby Mole (1/1000)
Automatically banks clues for you. (1)
Hellpuppy (1/1000)
All ash drops will be noted. (1)
Kalphite Princess (1/1000)
You cannot be poisoned or envenomed by NPCs (1)
Dagannoth Prime (1/1000)
Gives a +5 magic attack bonus per level. (3)
Dagannoth Rex (1/1000)
Gives a +10 melee and ranged defence bonus per level. (3)
Dagannoth Supreme (1/1000)
Gives a +5 ranged attack bonus per level. (3)
General Graardor (1/1000)
Increases damage by hammer and maul-based weaponry by 5% per level.(3)
Kril Tsutsaroth (1/1000)
Increases damage by blood spells by 5% per level (3)
Kraken (1/1000)
Water runes will not be required for spells. (1)
Kreearra (1/1000)
Increases damage by crossbows by 3% per level (3)
Smoke Devil (1/1000)
Fire and air runes will not be required for spells. (1)
Snakeling (1/1000)
Magic attacks have a 10% chance per level to envenom the target. (3)
Ranged attacks have a 10% chance per level to envenom the target. (3)
Melee attacks have a 10% chance per level to envenom the target. (3)
Zilyana (1/1000)
Gives a +15 magic defence bonus per level. (3)
Prince Black Dragon (1/1000)
Acts as partial dragonfire resistance, with maximum at level (2)
Scorpias Offspring (1/1000)
There will be a 50% chance that a Larran's key drop will be doubled. (1)
Vorki (1/600)
Acts as a Salve amulet without needing to wear one. Level 2 acts as the Salve amulet (ei) (2)
Venenatis Spiderling (1/500)
You will receive 5% more blood money per level on player kills. (3)
Chaos Elemental (1/500)
You can teleport at any level of the Wilderness outside of combat (1)
Vetion Jr (1/500)
Bones used at the Wilderness Chaos Altar will award 4x experience.(1)
Callisto Cub (1/500)
Gives a +5 crush bonus per level. (3)
Runeby (1/500)
Shadow spells will deal 15% more damage per level. (3)
Dark Core (1/250)
Grants 10 + 2% lifesteal per level when your primary weapon is a spear. (3)
Corporeal Critter (Metamorph)
Grants 5% lifesteal per level when your primary weapon is a spear. (3)
TzRek Jad (1/100)
Adds +5 Ranged strength and +5% Magic damage bonus per level. (2)
TzRek Zuk (1/100)
Your double drop rate has a 5% chance per level to become triple drop rate. (3)
Phantom Hand(?/?)
Grants a 10% chance to receive an extra roll at the Brimstone Chest per level (?)
Skotos (1/65)
Ancient shard drop rate is doubled from the Kourend Catacombs. (1)
Dharok (1/150 from chest )
Grants a 5% damage boost per level when current hitpoints is under 10. (3)
Verac (1/150 from chest )
Grants a 5% chance per level to ignore the target's defence. (3)
Guthan (1/150 from chest )
Grants a 5% chance per level to heal 1/2 of the inflicted damage to the target. (3)
Karil (1/150 from chest )
Grants a 10% chance per level for the Karil's crossbow to ignore the target's defence. (3)
Ahrim (1/150 from chest)
Magic damage and accuracy is increased by 10% per level when wearing the full Ahrim's set. (3)
Torag (1/150 from chest)
The Dragon warhammer and Statius' warhammer special attacks will drain 3% more defence per level. (3)
Olmlet (1/1000)
Increases damage and accuracy by 5% per level while in a CoX raid. (?)
Phoenix (1/1000)
You will not take any residual damage from the Wintertodt. (1)
Larry (1/1000)
The Tome of Fire will not consume any pages when active. (1)
Falco (1/1000)
Deals 4% extra damage with darts and javelins per level. (3)
Lil Zik (1/500)
Provides a 10% chance per level that a special attack does not consume its energy outside of PvP situations (3)
Greater Demon (Wilderness Achievement Diary)
Provides 10% increased damage and accuracy to Demons (1)
Mimic (?/?)
Provides a 33% increased chance of receiving a mimic from a clue casket (?)
Bloodhound (1/1000)
Youngllef (1/500)
The Bow of Faerdhinen and Blade of Saeldor will have a 2% chance per level at healing 100% of the damage inflicted. (3)
Corrupted Youngllef (1/1000)
The Bow of Faerdhinen and Blade of Saeldor will have a 2% chance per level at dealing double damage. (?)