Symbiotic Swarm Its been a while since Ive come across an Abzan general that really excited me, but Kathril, Aspect Warper shares so much with Rayami, First of the Fallen a general I really enjoyed out of Commander 2019 that Im willing to bet that lightning strikes again here
Serah is going to do a lot of work
The fact that it serves as an overcosted Shock than can destroy whatever swords Sram, Senior Edificer is wielding against you is just bonus
There isnt much need to replace basics with cards like this in Commander, but if the secondary effect is something your deck actually cares about, you might take a second look
The Aura + Venture is going to be good enough for that, and then the completed dungeon bonus makes this far more potent
Use flicker effects to bring the engine in and out of play, to give multiple opponents boards full of -1/-1 counters and reuse its proliferate effect