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Weaponry: Why a floating crystal? If you wanted to give it a casting focus, adding a jewel to the hilt of the rapier would have worked. If you were bent on trick weapons, a small scepter to go paired with the rapier would have sufficed. Bonus being that you could use the scepter on its own to cast instant-spells where fitting and use it in
slightly interesting ways. If you need to cast a big spell, then you could combine scepter and rapier into a staff.
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Animations: Seeing that there's a second item involved, the stance looks silly. The Agrippa stance RDM is using is supposed to be for wielding the rapier by itself, since the offhand is behind you partly for balance, partly as a result of you turning your body sideways to give the enemy less of you for them to hit. There are dual wielding stances (for rapier and dagger) that could work, or could be modified to work with RDM.
There's also the issue of how the rapier and crystal are sheathed. The rapier should be sheathed on the left side, with the crystal being set either under the hilt or next to it (similar to how a buckler is carried with a sword/rapier). They're currently rigged like they were hand-to-hand weapons, which makes things look really weird.