Invoking the Great Spirits

In order to invoke you must first know the true name of a god, demon or great spirit.  This is well guarded information.  High priests and warlocks may know true names but common worshippers or clerics do not.  These names are often given in exchange for rigid oaths made to the spirit.  Spreading a spirit's name without permission is foolish.  

Howl's Moving Castle, Studio Ghibli

After speaking the spirit's name the invoker must make a short command or request.  For each word¹ used in this command or request the invocation's target number increases in difficulty by 2 (starting at base 10.)  The more words are used in the invocation, the more specific, focused, and powerful it is.

Each invocation requires a channeling focus.  The focus is what the spirit's magic flows directly through.  This must be a physical item relevant to the invocation performed.  

Invocations are immediate, present magic.  They cannot effect things at a great distance from the invoker or have long lasting active magical effects.

Howl's Moving Castle

Each great spirit has a set of domains (1-3 based on power.)  The invocation must fit within the domains of the spirit being invoked.  A fire demon cannot control anything outside of fire.  A god of hearth, home, and harvest cannot turn an enemy to stone.  

The invoker must have the same alignment as the spirit invoked or their check is made at disadvantage.

Failing an invocation prevents one from invoking for 3 days and causes immediate wild magic. 

¹ Except for a, an, the