Sadly we lost last week's episode which marked the end of Szithis the druid's reign in the undercity. The former mentor of Zola (the gorgon girl he'd taken under his wing) resurfaced, under the influence of the zombifying mutagenic disease known as Phyresis. Szithis was reaping what he sowed, having let that mentor die against the phyrexian agent in the last arc, and dumping her body into contaminated water. All so he could take legal guardianship of Zola and force his villainous nature into a heroic face heel turn, a move that simultaneously sentimental and selfish.
Unbeknownst to him, his murder victim was also an old druid of his former Selesnyan circle. This druid had plans for Zola that mirrored a failed ritual that had robbed Szithis of his sight and scarred him many years ago.
The now risen revenant druid kidnapped Zola from Szithis and spirited her away to sacrifice the child in a ritual to resurrect the living god of nature and vitality; Ma'at Selesnya. Szithis pursued with his friends in tow, and found a high stakes hostage situation. Seeing no other way out, he offered his own life in exchange for Zola's safety.
Szithis perished willingly, offering his lifeblood to the soil. Amazingly, the ritual worked and brought an avatar of Ma'at Selesnya into being, who began to cleanse the plane of what Phyrexian influence it could find, beginning with the revenant druid who had killed szithis and summoned the avatar itself.
Zola was traumatized by her mentor dying, and her spark ignited; causing her to planeswalk away.
Time passed, the party mourned their losses, and a newcomer arrived in Ravnica from another world: Ubbe, the barbarian from Kaldheim. He was tasked with defeating an oncoming Phyrexian threat, something the party was very familiar with by this point.
Speaking of Phyrexian threats, the party witnessed the avatar of ma'at selesnya have a kaiju battle against a massive Simic mutant on live TV. The mutant resembled both an eldrazi and a phyrexian, but also vestiges of former guild leader; Zegana the merfolk. Zegana felled the avatar, and it dropped into the undercity through a sinkhole. It seemed the Simic had come into possession of dangerous dna, and hadn't learned anything from the recent otherworldly incursions. Or perhaps they know all too well, having turned their former guild leader into a giant weapon at the behest of Vannifar, their new master.
This week, all that comes to a head! As our heroes go into the undercity, and then deeper; into the subterranean oceanic Zonot where the Simic scientists lair.
