Hydra and skel worker increase damage of physical attacks.
Metallic Sound is a magic spell. They do not improve its damage any more than they would improve thunderstorm or psychic wave.
As I have said before, metallic sound is a basic, vanilla spell. Tantamount to fire bolt, cold bolt, and lightning bolt. It is simple a multiple of your matk dealt as magic damage. If metallic sound had some weird unique crass, incorrent formula that ignored int from cards or matk for equipment but somehow still did magic damage, I would have said so, instead of telling you its basic like a firebolt and that cards that increased matk would make no sense if they didn't improve spells that are fueled by matk. It is safe to use some deductive reasoning here.
I Recommend spending a few minutes trying out a mage in game so you can understand the basic tenaments of magic using classes. A metallic sound performer functions the same.
Edited by Jaye, 23 May 2014 - 07:24 AM.