Welcome! It looks like an in interesting take. The lifegain from Harvester seems useful. One problem I see is the mana. According to this article, we need 13 R sources to have a 90% chance of casting a single color 2-drop on time and 16 B sources for Ob Nixilis on T5 (IIRC). So I would recommend more colored sources and maybe replacing Ob Nixilis with Chandra. Dual lands like Aether Hub and Canyon Slough are your friend.
I married red deck wins to mardu and excluded white from the party.
Creatures
4x Bomat Courier
1x Kari Zev, Skyship Raider
4x Earthshaker Khenra
2x Piz Nalaar
4x Ammit Eternal
3x Hazoret the Fervent
4x Scrapheap Scrounger
Spells
1x Fatal Push
1x Key to the City
4x Unlicensed Disintegration
4x Aethersphere Harvester
1x Skysovereign, Consul Flagship
1x Ob Nixilis Reignited
Lands
4x Ramunap Ruins
8x Mountain
9x Swamp
1x Westvale Abbey
2x Sunscorched Desert
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.