Let's start with the most important information first:
No SD
Name | Fire | Water | Wind | Light | Dark |
Fairy | X | ||||
Garuda | X? | X | |||
Harpu | X | ||||
Inferno | X | X | X | ||
Inugami | X | X | X | ||
Magical Archer | X | X | |||
Warbear | X? | X | |||
Werewolf | X | X |
2**
Name | Fire | Water | Wind | Light | Dark |
Fairy | X | X | |||
Garuda | X | X | X | ||
Harpu | X | X | |||
Hellhound | X | X | X | ||
Howl | X | X | X | X | X |
Imp | X | X | X | X | X |
Pixie | X | X | X | X | X |
Salamander | X | X | X | X | |
Warbear | X | X | |||
Vagabond | X | X | |||
Viking | X | X | X | ||
Yeti | X | X | X | X |
3***
Name | Fire | Water | Wind | Light | Dark |
Bearman | X | X | X | X | X |
Fairy | X | X | |||
Golem | X | X | |||
Griffon | X | X | |||
Harpy | X | X | X | ||
Harpu | X | X | |||
Hellhound | X | ||||
Inferno | X | X | |||
Inugami | X | X | |||
Magical Archer | X | X | X | ||
Salamander | X | ||||
Serpent | X | X | X | ||
Warbear | X | ||||
Werewolf | X? | X | X | ||
Vagabond | X | X | X | ||
Viking | X | X | |||
Yeti | X |
OTHER VALUABLE MINIONS
Elemental DARK (not high elemental, not low elemental) - dark/light scroll / wish temple
Epikon Priest ALL - mystic scroll / wish temple / unknown scroll
Fairy LIGHT - invite 50 friends by facebook / Secret dungeon
Farmable Monsters:
Inugami FIRE - Faimon Volcano / Unknown scroll / Mystic scroll
Inugami WATER - Garen Forest /Unkown scroll / Mystic scroll
Inugami WIND - Telain Forest /Unkown scroll / Mystic scroll
Inferno FIRE - Vrofagus Ruins / Unknown scroll / Mystic scroll
Warbear WATER - Mt. White Ragon / Unknown scroll / Mystic scroll
Werewolf FIRE - Vrofagus Ruins / Unknown scroll / Mystic scroll
Grim Reaper WIND - 1st new area 10/28/2014 / Unknown scroll / Mystic scroll
Other 4*, 5*, 6* monsters can be summoned by mystic scroll, summon by crystals, event dungeons, wish temple ?
Other light/dark monsters can be summoned only by light/dark scroll or wish temple.
Credit for this information is to com2us forum member "rzechu".
Here is the original forum post for credit as well.
If you know about a secret dungeon that is not in the list above, leave a comment below so that I can update this information.
*** 10/28/2014 Update ***
The four new campaign areas that opened up today will allow for more farmable monsters. I will update as soon as I have unlocked them all.