[Fern]

That could be abusable with Fruit of Fluidity.

As for Amalgama in general, I would rather just give them a completely new interaction with Sanctity that simulates a better use of their Formidable passive. They're essentially spirit dolls anyway.

"There is also a Scaled SAN% + Scaled LUC% chance, while you are possessed by spirits, that damage higher than your current HP will leave you at (Character LV) HP instead, but a random spirit will leave from your possession."

Most people (including myself as an Amalgama player) really don't like losing spirits (in part because they're not that easy to get), and some of the Amalgama skills even require you to be at specifically 5 spirits. I feel this wouldn't be a good idea.