Welcome! I'd love to help, but this section of the forums is dedicated to Standard, which includes only cards more recent than Fevered Visions from the quarterly run of storyline sets. I am not sure which Ob Nixilis you mean, as none of the four that this search reveals (https://www.mtggoldfish.com/q?utf8=✓&query_string=ob nixilis&set_id=&commit=Search) seem to have obvious synergy. I will move this inquiry to someplace that Fevered Visions is in scope, but you may want to specify which version of Ob Nixilis you mean.
RNA Standard: Grixis Midrange, Jund Deathwhirler, Sultai Vannifar
GRN Standard: Red Midrange, Mono-Blue Tempo, Wr Aggro, Gruul Experimental Dinosaurs, Sultai Midrange, Jeskai Midrange
Modern: Bant Spirits
Forcing a single archetype in all formats: too many colors, bad mana.