I've realized over the last few days that, by making the Songs' arcane abilities completely exempt from the limitations imposed by the hosts' abilities, I inadvertently made it a no-brainer to just have the Songs advance purely in their arcane abilities, effectively giving Devas double-rate advancement, which is what I meant to prevent by limiting Songs to only be able to take advances that their current host already had.
On the other hand, the reason for the arcane abilities exemption was so that hosts don't have to try to duplicate the Song's arcane development first, before the Song can improve in that area.
To resolve this, I've just updated the "Chord Progression" setting rule on the wiki. The new version is:
* Chord Progression (custom): A player's Song and host each receive full XP awards. The host advances normally in all respects. The Song may spend Advances normally to gain abilities (Traits/Edges) which the host possesses, based on the Song's Attributes. The Song may also purchase arcane abilities not possessed by the host, but at double cost. If two Advances are required, one must be paid by the Song, but the other may come either from the Song or the host. e.g., If you wish your Song to gain Faith d8, the base cost is half an Advance if the Song's Spirit is d8 or higher, or a full Advance if the Song only has Spirit d4 or d6, regardless of the host's Spirit. This cost is then doubled (to either one or two full Advances) if the host does not possess the Faith skill at d8 or higher.
The reasoning behind this is that, if your Song and host both have, say, Spirit d6, and you want to improve your Song's Spirit to d8, then the original Chord Progression rule required you to spend two Advances: First the host spends an Advance to get Spirit d8, which then raises the limit on how high the Song can go, allowing it to also get Spirit d8. The new version of Chord Progression applies this same cost to, e.g., learning a new Power when you have a non-spellcasting host.
Out of fairness, this change is not retroactive. If you have any unspent Advances, you can still spend them under the old version of the rule.
God45 skrev:The newest journal entry from Spellbutcher is posted

I am going to re-post this one part that you guys might find intressting...
On a stranger note I seem to have developed green spikes that are sticking out of my forearms. They seem to be of the same type that the spikemonster who scratched me had. I also seem to be able to fire them in a manner similar to the spike monsters.

Speaking of arcane abilities and interesting ideas... Have you considered trying to build this using the Natural Weapons Edge from Savage Armoury instead of (presumably) taking it as a power? Doing it with Natural Weapons, you'd almost certainly end up with a much shorter range and you'd have to spend an action to pop out a new set of spikes after firing them, but it would also mean that you don't have to spend PP on them and they may also be usable as a melee weapon (depending on how you build them).
I post in English, but can read Swedish. When replying to me, either language works.