Ooh forgot about the 'spell damage' part.
Though it fits in with the weapon that has been created, there are currently no 'magic weapons'.
The 'magic weapon' part has a problem. First, as you said, it instantaneously becomes vulnerable against the indestructible mirror shield (although it is good that such a specific card has a counter). Secondly, if your opponent does not have the mirror shield, the 'magic weapon' can simply bypass any shield (and additionally is NOT affected by sundial or any current creatures' skills). Yes, Titan has momentum and 7 attack per turn, but it is considered OP especially due to its health, AND dealing 7 damage per turn is not really the same as dealing 25 damage all of a sudden.
I thought that the momentum effect of this (and the one I specifically mentioned two posts ago) was too powerful. I thought of an interesting additional ability may be to have a certain small chance to destroy the shield when attacking with a certain number of charges (-25% of course) but I don't think anybody will like a haxxor thing like that.
EDIT: Just saw the changes you made to the first post. Thanks for giving me some credit
Anyways, the unupgraded version should have 1
cost increase instead of 1
ability cost increase, or it is really too expansive.
You may want to explain a bit further in an organized manner on your 'magic weapon' and 'charge'
(I hope you change the art soon
)