For starters, it's a hybrid design, which means it has to overlap abilities found in black and green
Any abilities that trigger as the permanents enter the battlefield this way won't be put onto the stack until after Genesis Ultimatum has finished resolving and is in exile
When Grakmaw dies, create an X/X black and green Hydra creature token, where X is the number of +1/+1 counters on Grakmaw
Cards like Phytotitan, Malignus, and Daemogoth Titan are all great targets to be sacrificed to Ziatora in order to deal some real damage, The treasures generated by Ziatora also enable you to work some artifact synergies into your deck, or even pull off a Revel in Riches win
Both seem like they're designed as MTG commanders, but while Rakdos is doing his Standard sacrifice shenanigans, Aurelia gets you bonuses when everyone swings with a bunch of creatures
A single board wipe would not only reset the battlefield, but remove all of your acceleration