I’m not using the full Spellsinging rules from the ACKS Heroic Fantasy Handbook in my Black City campaign, but I like the concept that the revised Magical Music proficiency should be based on spellsinging.
Here’s what I’m going to use:
Magical Music: The character gains a limited ability to spellsing. The character adds one spellsong in his repertoire, which he casts as a 1st level spellsinger. A character can select this proficiency multiple times; each rank adds another spellsong to his repertoire.
Casting a spellsong normally requires 1 turn (10 minutes) and the spellsinger must succeed a special Performance proficiency throw to cast a spellsong. The character adds his Charisma modifier to this check.
(Non-proficient Characters will need to roll 18+, so Performance is a de-facto pre-requisite for Magical Music.)
He will need to be able to move his hands and sing freely in order to perform a spellsong. (Instrumentalists will need their instrument instead of singing.)
If the Performance throw is successful, then the spellsong takes effect at the end of the turn. On a failed throw means, the spellsong does not take effect. The spellsinger suffers no ill effects from failure, but cannnot try again until the next day.
If he has enough time, the character can attempt a methodical spellsong, taking 6 hours to elaborately prepare and stage the performance. This grants a +4 to the Performance throw. Failure incurs the same results as a standard spellsong.
A Spellsinger can also attempt a hasty spellsong (taking 1 round), but with a -4 penalty on his Performance throw. If the result is a natural 1, then a mishap may occur. Make another Performance throw with the same -4 modifier; if this results in failure, then the spellsinger suffers a mishap and must roll 1d10 on the Spellsinging Mishap Table (use the Minor Mishap column).