Cenedril Guide
To complete your prequests go to the Hall of the Eye of Windom, in Varanas.
There are some Eye of Wisdom Mage NPCs there, find Hagris Rya (58.4, 62.3) to collect your first quest and learn more about the Mirrorworld.
Completing ‘Wish to travel to Mirrorworld’ will unlock the quests from Aylin Shin who give you 2 more quests, ‘Memento to the Mirrorworld’ and ‘The Mirrorworld Beckons’. After completing these quests you are done with the previous quests, congratulations!
To enter Mirrorworld you will find a new button in the top left corner of the screen, next to the character picture, click on it to open the Mirrorworld interfaz.
There are free instances of Mirrorworld changing every day but you can buy a Mirrorworld Ticket in Item Shop to access the non-free ones too or repeat.
You can find more details about free instances per day below (info from Int's post):
Monday:
Steadfast Mirror heart of the Ocean (2)
Steadfast Mirror Shrine (8)
Steadfast Mirror Dreamworld (14)
Dynamic Mirror Wyrm Lair (16)
Mystical Mirror Crypt (21)
Tuesday:
Dynamic Mirror Shrine (1)
Dynamic Mirror Caves (7)
Dynamic Mirror Sewers (13)
Mystical Mirror Hall (18)
Steadfast Mirror Castle (20)
Wednesday:
Dynamic Mirror Altar (4)
Dynamic Mirror Corridor (10)
Mystical Mirror Nest (12)
Dynamic Mirror Laboratory (19)
Steadfast Mirror Castle (20)
Thursday:
Steadfast Mirror Ruins (5)
Steadfast Mirror Chamber (11)
Mystical Mirror Pirate Ship (15)
Dynamic Mirror Wyrm Lair (16)
Mystical Mirror Crypt (21)
Friday:
Steadfast Mirror heart of the Ocean (2)
Mystical Mirror Tower (6)
Steadfast Mirror Shrine (8)
Dynamic Mirror Corridor (10)
Dynamic Mirror Sewers (13)
Mystical Mirror Hall (18)
Steadfast Mirror Castle (20)
Saturday:
Dynamic Mirror Altar (4)
Mystical Mirror Fortress (9)
Steadfast Mirror Chamber (11)
Mystical Mirror Nest (12)
Steadfast Mirror Dreamworld (14)
Steadfast Mirror Library (17)
Dynamic Mirror Laboratory (19)
Sunday:
Dynamic Mirror Shrine (1)
Mystical Mirror Water Cave (3)
Mystical Mirror Tower (6)
Mystical Mirror Fortress (9)
Mystical Mirror Pirate Ship (15)
There are different Cenedril Pets :
Dynamic Cenedril (red):
Liphisto - (Dexterity + Physical Accuracy)
Mayi - (Physical Attack + Dodge)
Alis - (Dexterity)
Solar - (Physical Crit. Hit Rate) + Dodge)
Tatuin - (Physical Attack)
Sharpor - (Dexterity + Physical Attack)
Belorg - (Physical Crit. Hit Rate + Magical Crit. Hit rate)
Steadfast Cenedril (Green):
Bendor - (Strength + Physical Defense)
Salo - (Staina + Physical Defense)
Forensa - (Strength)
Razor - (Magical Defense + Parry Rate)
Ardes - (Stamina)
Onid - (Stamina + Maximum HP)
Tarabeth - (Strength + Physical Attack)
Mystical Cenedril (blue):
Mersi - (Wisdom + Magical Attack)
Wolin - (Intelligence + Magic Accuracy)
Shados - (Wisdom)
Topex - (Magical Attack + Magical Crit. Hit Rate)
Garsit - (Intelligence)
Azael - (Bonus Heal Points)
Skormor - (Intelligence + Magical Attack)
You can get cenedril hearts running Mirrorworld instances, (according to Cenedril type), and using 50 hearts - they must be the same type - you can summon a Cenedril Pet and equipping 2 different Cenedril will give you a special skill. Combine Cenedrils from slots I and II to get them all.
It is possible to increase the Cenedril level by farming items from Mirrorworld instances.
The first Cenedril rank is made up of 10 levels and each increased activates an additional 10 more levels. There are 100 levels total.
To use correctly your Cenedril skills, keep in mind your class
Example:
If you have a healer class, may combine Onid (Stamina + Maximum HP) and Azael (Bonus Heal Points) to get the skill Spirit Illusion (Increase Healing by 100)
If you have a Physical DPS class, combine Sharpor (Dexterity + Physical Attack) and Onid (Stamina + Maximum HP) to get the skill Burning Aggression (Increase Physical Damage by 15)
If you have a magic class, combine Skormor (Intelligence + Magic Attack) and Belorg (Physical Crit. Hit Rate/Magical Crit. Hit Rate) to get the skill Prayer of Destruction (Increase Magical Damage by 15)
If you class is a tank, combine Onid (Stamina + Maximum HP) and Salo (Stamina + Physical Defense) to get the skill Burning Aggression (Increase Physical Damage by 15)
But there are many other pets combinations to get different skills.
I hope my little guide can help those who join CoA to learn a bit more about the Cenedril pets. I'm sure I have many more things to explain and gonna to add them too later, or if someone wants to add them, please feel free to do so!
If you need help or have questions, feel free to whisper me 
Greetings
Onlyagul
