If you like beasts, then it is a good idea to invest some time in creating a Beast Master. Beast Masters give all beasts in their unit a 15% boost in attack power. Beast Tamers also give this boost, but only a 10% one. 
All beasts, with the exception of the Hellhound and Cerberus, can fly. This ability makes them useful in Vultan/Raven teams. Flying teams travel faster than all others, so this combo can greatly help your army.
Beasts are 'Large' characters. They take up 2 character slots on a team, meaning you can only have a maximum of 2 on any given squad.
Lastly, if you wish to upgrade your beasts you must have it level up in battle during a mission after it has obtained all necessary status requirements.  
Picture
Zargata 2012

Griffin Line

​Attacks: 
x2 Front, x1 Middle, x2 Back

Griffin
"A half-lion, half-eagle beast that attacks with powerful gusts of wind."
Leadership Rank: 
None
Terrain Advantage:
Sky
Carry: 3 Items
Note: The Griffin uses the attack 'Wind Shot' in the back row. 
Found in the Wild: 
Crenel Canyon I / Highlands / Level 3 
Zenobian Border / Highlands / Level 5 
Gunther Piedmont / Barrens / Level 7 
​Crenel Canyon II / Highlands / Level 9 
Mt. Ithaca / Highlands / Level 13
Drops: Power Fruit
​Attacks: 
x2 Front, x1 Middle, x2 Back
Note: The Opinincus uses the attack 'Wind Storm' in the back row.

Opinincus
"Flying beast with characteristics of a lion, an eagle and a bear."
Leadership Rank: 
None
Terrain Advantage:
Sky
Carry: 3 Items
Class Change Requirements: ​
MEN 105+, AGI 127+, DEX 91+
Found in the Wild: 
Celesis / Snowy Plains / Level 20 
Temple of Berthe II / Highlands / Level 22 
Romulus / Barrens / Level 24 
​Tybell / Highlands / Level 30 
Mt. Keryoleth II / Highlands / Level 34
Drops: Angel Fruit, Crystal of Precision or Stone of Quickness

Wyrm Line

​Attacks: 
x2 Front, x2 Middle, x2 Back

Wyrm
---
Leadership Rank: 
None
Terrain Advantage:
Sky
Carry: 3 Items
Found in the Wild: 
Tenne Plains / Barrens / Level 2 
Mylesia I / Highlands / Level 5 
​Volmus Mine II / Highlands / Level 6 
Mylesia II / Highlands / Level 11
Drops: Power Fruit
​Attacks: 
x2 Front, x2 Middle, x2 Back
Note: The Wyvern uses the attack 'Fire Breath' in the back row.

Wyvern
"Large flying beast that is more powerful than a Wyrm. It is capable of spewing fire breath."
Leadership Rank: 
None
Terrain Advantage: 
Sky
Carry: 3 Items
Class Change Requirements: ​
STR 140+, AGI 124+, DEX 102+
Found in the Wild: 
Temple of Berthe II / Barrens / Level 22 
Tremos Mt. I / Highlands / Level 23
​Latium / Highlands / Level 31 
Wentinus II / Highlands / Level 34
Drops: Cup of Life, Champion Statuette or Angel Fruit

Hellhound Line

Leadership Rank: 
None
Terrain Advantage:
Mountains
Carry: 4 Items
Attacks: 
x3 Front, x2 Middle, x1 Back

Hellhound
"Two headed canine with sharp fangs and powerful jaws designed to tear its enemy's flesh."
Found in the Wild: 
Crenel Canyon I / Forests / Level 3 
Zenobian Border / Barrens / Level 5 
Alba / Barrens / Level 8
​Crenel Canyon II / Forests / Level 9 
Highland of Soathon / Barrens / Level 11
Drops:
Power Fruit
Leadership Rank: 
None
Terrain Advantage:
Mountains
Carry: 4 Items
Class Change Requirements: ​
STR 139+, VIT 138+, MEN 90+
​Attacks: 
x3 Front, x2 Middle, x2 Back
Note: Cerberus uses the attack 'Mesmerize' in the back row.  

Cerberus
"Three-headed canine, known as the gatekeeper of hell. Its piercing eyes instill fear in its enemies."
Found in the Wild: 
Gules Hills I / Forests / Level 16
Gules Hills II / Highlands / Level 23 
​Barpheth / Barrens / Level 27
Drops: Angel Fruit, Goblet of Destiny or Flag of Unity

Other Beasts

​Attacks: 
x2 Front, x1 Middle, x2 Back

Cockatrice
"Dreaded beast with the body of a rooster and a snake's tail. Its petrifying breath turns opponents to stone."
Leadership Rank: 
None
Terrain Advantage:
Sky
Carry: 4 Items
Note: The Cockatrice uses the attack 'Petrify' in the back row.
Found in the Wild: 
Audvera Heights / Forests / Level 12 
Mt. Keryoleth I / Highlands / Level 15 
Temple of Berthe II / Snowy Highlands / Level 22 
​Romulus / Highlands / Level 24
Mt. Keryoleth II / Barrens / Level 34
Drops: Revive Stone or Scroll of Discipline
​Attacks: 
x2 Front, x1 Middle, x2 Back
Note: The Sphinx uses 'Evocation' in the back row. This attack is similar to Dark Quest.

Sphinx
"Monster with wings of an eagle, the upper body of a human and lower body of a lion. It has innate knowledge of magic."
Leadership Rank: 
None
Terrain Advantage:
​Sky
Carry: 3 Items
Found in the Wild: 
Argent / Snowy Forests / Level 29 
Latium / Highlands / Level 31 
​Mt. Keryoleth II / Highlands / Level34
Drops: Angel Fruit or Altar of Resurrection
Ogre Battle 64 and all related material is (c) Quest/Nintendo/Atlus/Square Enix
Last Update: 07/06/20
Portrait Image Rips By Titan of Ether, GWChapman, and Relaie
Addition Information found at: Ogre Battle 64: Neutral Encounter Guide, OB64 Mod Notes by GWChapman