Catalog entry at the Musée de la musique in Paris

This is a roughly cello-sized instrument with 6 playable strings and 12 sympathetic strings, 18 in total. The catalog labels this instrument a "Viola Bastarda" which usually means a virtuosic and aggressive playstyle on a regular Viola da Gamba, not a type of instrument.

https://en.wikipedia.org/wiki/Viola_bastarda

Sound sample of the bastarda playing style on YouTube

The soundholes in the form of flaming swords, the rosette, the sympathetic strings and the blindfolded head on the pegbox suggest that this instrument is part of the "d'Amore" family, a Bass Viola d'Amore.

https://en.wikipedia.org/wiki/Viola_d%27amore

So far I haven't found another instrument like this, maybe it's unique?

damn i don't know how much you'd have to pay me to change strings on that thing, but it would be a lot

It's a real bastard to tune.

...not a type of instrument.

From the Wikipedia article you linked:

Viola bastarda refers to a highly virtuosic style of composition or extemporaneous performance, as well as to the altered viols created to maximize players' ability to play in this style.

Early sources speak of the viola bastarda as a style of playing, and the ranges of pieces written during this time indicate that bastarda pieces were played on whichever size viol was at hand; however, Rognoni describes the standard size of a viola bastarda as between that of a tenor and bass viol, indicating a change in understanding of the term.

Oops! I might have overread that...
Thanks for the correction!

Points for the weird, unsettling head

That's a sexy instrument