Reviewing all the topic,
All the card effect is confusing, look that:
Basicaly I think that GTB blocks things that use your MATK as damage and MDEF to reduce damage.
Priest buffs and healing do not use MATK. So, this is not a good conclusion about the card.
That was a general rule that applies to offensive skills. Of course we can't say that it's universally correct since there are skills such as dispell and soul burn that don't use MATK or MDEF and they're still blocked.
But that gives a general idea on what GTB block, if you want to I can list all the skills GTB blocks because there isn't a one universal rule to cover all of them. There are basically only certain types of attacks in the game. Melee, ranged, and magic, then support skills Physical support, magical support. I'm guessing that in the code of each skills there's a line that defines on which category they go into. And GTB blocks everything going into the "magic" category. That's the only unviersal rule there is, other then that you can only list the skills it block or create some overly complicated rule.
GTB blocks attacks that use your MATK as damage and MDEF to reduce damage PLUS offensive & defensive support skills (Dispell, Soul Burn, Priest Support skills, including Lex Divina. It is blocked by GTB.). I don't know about songs.
As for this, GTB does not block energy coat, any of the BS buffs nor Paladin buffs. GTB doesn't block any skills that are used on your without targeting symbol. Nor does it protect you from status effects and some of them are indeed MDEF based. And songs are not blocked, they're not considered magical.
