I delved into biblical horror for this one, as (spoilers) The Abbot from CoS:RRL isn't really a deva anymore, but a fiend, duped and seduced by the Dark Powers into devising its own plan to free Strahd and Barovia. Doomed from the start, The Abbot's plan and powers are revealed to the PCs, as well as a form that more accurately depicts what the Dark Powers have made him into.
I based this image off of old monastic illustrations of cherubim (not cute little angel-babies, but the four-headed, six-winged angels used as messengers). The multiple animals depicted on cherubim resonated to the Abbot's obsession with splicing multiple animals onto all the Belviews, speaking to some twisted aesthetic. The rest is mostly inspired from Dragnacarta's creature stat block and my love of FromSoft's monster designs.
Hope you enjoy.