You can only contract a very specific number of enemies while having a summoning bottle in your item inventory (I am not sure if the item just need to be in anyone's inventory or in the summoner's, I put it in the sumoner's just to be safe).
If you defeat the contractable enemies you have a chance to contract it, the chance is pretty high except for the Stone Golem who took me like 6 tries (maybe I was unlucky).
The summoning bottles are sold in many shops. The Lv9 summons need a Large Summoning Bottle that can only be found in the last dungeon.
Monster that can be contracted from lowest summoning level to highest:
| Lv 1 | Slime | Giant Bat |
| Lv 2 | Fairy | Cold Wisp |
| Lv 3 | Vorpal Hamster | Harpy |
| Lv 4 | Unicorn | Electric Rat |
| Lv 5 | Salamander | Siren |
| Lv 6 | Lamia | Apprentice Succubus |
| Lv 7 | Succubus | Stone Golem |
| Lv 8 | Queen Spider | Elder Succubus |
| Lv 9 | Greater Demon | Black Dragon |
Summoning is useless most of the time. It's only useful for a late game quest and trophies (complete all quest and contract every summonable monster). Especially since you can recruit mercenaries and they take the same spot. The mercenary named Magus is a very powerful mage who can cast Demonic Flare around lv30, way more useful than most summons in the game.
Summoned monster that are mildly useful:
Cold Wisp. Just set its AI to only use skill and you will have an AoE freezing attack every turn.
Black Dragon so you can use possession with your Summoner to imitate its attack, however at that point in the game your party is probably strong enough to win most battle with just auto attack.
The best summoner you can find is probably the premade character at the unlockable town since she can use every type of magic.
PS: There is a merecenary that also has summoning skill so you don't even need to create your own summoner. Her name is Mystic and you can recruit her by beating the Amazon in duels and asking for a member as your reward. I got her by beating the Amazoness 4 times, I don't know if I was unlucky or if their recruitment pattern is set in stone.
There are 10 recruitable mercenaries
5 from Wild Bull
4 from Amazon Team
1 from a late game area (an angel valkyrie you can recruit if you talk to her).