There's a number of ways Gretkov could be doing this, but I think the Matrix Agent explanation is the simplest one. That suggests that this is a Spirit 4 effect, perhaps with conjunctional matter/forces/ effects to recreate his chosen equipment. Gretkov isn't actually here, and may no longer exist as a physical entity, rather he has become an EDE or- far more likely, has an EDE integrated with him that allows him/it to use the spirit 4 effect 'bridge' or 'channel' to overlay onto a compatible being. It is effectively possession, though I maintain doubts that it is unlimited in scope. In all likelihood, he is limited by the number of eVictors in the vicinity. They probably have some sort of hardware installed to make them appropriate targets for this effect.
There's also likely a time 2/entropy 2 predictive effect in operation here, that switches which eVictor he is manifesting from whenever one would die, or alternatively, eVictors have achieved the ultimate goal of mass produced soldiers and are sufficiently identical in their pattern that all that would be needed to switch manifestations would be for the underlying pattern to deviate- at which point it would no longer qualify for the targeting effect and the switch would occur automatically. However this usage is getting really far into the metamechanics of the game, and I'm uncertain if it is likely to be the solution. It depends on how much work Auto-chan has put into figuring out Magick, and whether or not this effect is True Magick (as performed by mages) or a spirit effect. There's some overlap, and sufficiently powerful spirits are capable of pretty much anything, but there are some things they just can't do easily.
I would expect that, duplicating his gear and having made preparations, Gretkov probably has some kind of device on him that he can use to make someone into an appropriate target for the possession effect. Well, unless Auto-chan lied and/or didn't tell him how his new powers worked, both entirely possible. If getting nerf imprinted or whatever isn't a concern, then we really just need to eliminate all the eVics in the vicinity. That won't guarantee a kill, because he may not even actually be here, but instead wherever he's broadcasting from, but it would likely allow for the temporary elimination of Gretkov as a threat, since he'd need to either transit whichever body he's in back to the location from wherever he respawned, or just not come back at all.
If we had some sort of dSci or Spirit expert on hand, they could probably figure out what he's doing and act to counter it, but our two experts are currently in the Umbra dealing with some Voids ready to push the button. And honestly I don't think pushing The Button is the right choice here.
Instead my proposal is this:
[X] Yeah no, you're not killing a bunch of people just because it's inconvenient. Do you have another way?
|_[X] The bomb is an impressive weapon, but the threat to the human population is too high, particularly given that a number of the members of our team have cybernetics of various types and would be aversely affected. Instead, we hold the bomb in reserve, have the Voids focus on destroying the jammers, and send Kessler and Cross planetside to locate the local relay and call in firesupport.
Jumping between the Umbra and the Earth will do a number on Enlightened Personnel, and we can't risk more damage. Fortunately, there's a solution. Basically Kessler and Cross ride their hijacked titans down to Earth. This is a spirit/Dsci effect that shields them with the spirit, the Anomaly will shred the spirit and leave them unharmed. This is typically frowned upon by Dreamspeakers and may get you chased by angry spirits- but those are usual spirits and those who care about the natural way of things. These spirits are highly focused artificially made constructs that we've hijacked. None of those ethical considerations should even begin to apply when dealing with them.
It's not quite surfing the Mir back to land, but it definitely stands to be pretty awesome.
