Question: Can you only have one instance of certain summons?

[Redeyes]

There's a few spells like this, but most give you one of a few possible summons. If another player manages to summon a being before you you can't get it.

There's 3 elemental queens of water and 3 of air. There's 2 kings of earth and 2 of fire. You can also summon Anthrax, the banefire king, with death, and the earth king Father Illearth with blood.

Some blood summons also work like this, there's 6 Ice Devils, 5 Arch Devils, 4 Heliophagus, and 4 Demon Lords.

You can get one of 6 Spenta when using Call Amesha Spenta. Hinnom can get one of 6 different Grigori when using Release Lord of Civilization. Mictlan can get one of 4 Tlaloques when using Summon Tlaloque. C'tis can summon the Devourer of Souls. Sauromatia and La Pythium can summon the Daughter of Typhoon.

I think that's all for Vanilla, but mods can add more. CBM adds a few (three for Agharta summoned with Open the Seal. One with the fire ritual "Quest for the Firebird", although I think that one might use a somewhat different mechanic).