Raven tombs are kinda obscure nowadays, you think giving them a refine would help bring them more use? Something like an extra 2 attack, and built in TA3? (or TA4 for 40%, death blow 4 exist, why not this) so 13 base attack, and built in Triangle Adept 3/ 4 if they make it
I don't think they would give an added effect on non prf weapon refinement, at max they could give a buff nullifying effect against colorless.
Even if they make Raven tomes refinable I don't think they will become that usefull as archers are not that common in the current meta and we have so many units with high defences that can tank colorless and many other things (mainly armors) while Raventomes are usefull only against archers and daggers
I don't think they can give built-in TA 3 on top of a refine's stat boosts, that's a little much.
The raven tomes would be used more if they could be refined, right now they just represent a bit of opportunity cost. (They are useful enough though, they can help a flier mage reverse the weakness to arrows, they can help dancers function or gain bulk, etc.)
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