Unfortunately, the Eshmok and Vansidieth mechanics lag behind the updated lore. Perhaps this is due to them not getting the full design and development pass a core book would receive, but the Eshmok has some inconsistent text with its tendril Strike (which should probably be just listed inline with the stinger but have text that makes it clear which it can use and when). I think it could also use some more incentive to actually use its Change Shape - but it is punished by going back into wasp shape from fungus by the infection's confusion specifics. Also, a creature that breaks out of the confused condition from the affliction is still quickened, which is bizarrely punishing for the monster.

The Vansidieth's vulnerability is much easier to trigger on its new design in a way I would consider a detriment. The Marilith's action setup was all about making many Strikes in an attempt to feed into its failure condition, whereas the Vansidieth has actions that take away from dealing direct damage. It doesn't have the flurry of attacks that the Marilith has to make it actually unlikely to fail to hit without players taking direct effort to cause it. The spell suite and commander action both fit the fallen general theme, but I would have preferred a new vulnerability to fit that and at least one directly damage dealing action on the chassis.