Certain spells in Arkham Horror can only be cast on upkeep. One example is "Voice of Ra":
Upkeep Phase: You may cast and exhaust to gain +1 to all skill checks for the rest of this turn.
The rules state:
During the Upkeep Phase, each player takes the following actions, in order.
- Refresh Exhausted Cards
- Perform Upkeep Actions
- Adjust Skills
The Adjust Skills action states:
Finally, each player may adjust his investigator’s skills using the three skill sliders he placed on his investigator sheet during game setup. This process, as well as a general description of how skill sliders work, is explained in the “Adjusting Skills” diagram.
Casting a spell doesn't fall into any of those categories. I suspect that these are the things you must do on your upkeep, but you can also do additional things, such as cast spells. But the use of the word "Finally" in the Adjust Skills action could mean that this must be the last thing you do during your upkeep, although I don't think that is the case.
When during your upkeep can you cast upkeep spells? Can I cast them even before the Refresh Exhausted Cards action? In the case of "Voice of Ra" this would allow me to cast it twice in once turn.
Answers so far have said that casting spells is a mandatory upkeep action. This may be the case, but I still think the rules are ambiguous about that. The rules for upkeep actions state:
After refreshing his exhausted cards, each player must review his investigator’s cards to see if any of them have an Upkeep action. Each player must perform all Upkeep actions listed on his investigator’s cards every turn.
You are not required to cast Voice of Ra every turn. Therefore, Voice of Ra is not an upkeep action. This makes no distinction between optional and mandatory upkeep actions. The text of Voice of Ra however may make the casting of it optional. This too seems a little ambiguous. Even if this is the case, how are spells that are castable during "Any Phase" treated. Can they therefore not be cast during the upkeep (even though upkeep is a phase) because they don't have an upkeep action?
Also, if spells must be cast during the upkeep action, it means you will not be able to adjust your skills before casting. It seems a little strange to me that a spell you are casting this turn must be based off last turn's skills.