Finally jumping in from the GITP boards...
'No casting on another's turn' I think is pretty straightforward, based upon the Thinkagrams etc. that float around in direct contravention of a strict reading of that rule. You cannot cast in a way that substantively alters other units. The links atteSmythe provided spell this out well. Jack could have veiled *himself* while in a stack of dragons when Jillian arrived in that panel, but not floated illusory duplicates or hidden dragons as trees. A Shockmancer could not have fired a bolt at Jillian, but could perhaps have cast a spell on himself to the tune of 'If anyone touches me, blast with a stun discharge'. Healomancer, surrounded himself with a 'Healing aura for myself or anyone who touches me'.
The Turnamancy trick here obviously has some major mitigating factors going on here. It does seem consistent with the outlined speculation on the wiki.
Both of these are consistent with the idea of the Turnamancer "storing" their turn on the first turn, then granting the stored turn to the city on the next turn. This may be how Turnamancers do it. Turnamancers may also be able to "steal" another unit's turn in battle, effectively paralysing both units.
Turnamancers may be able to store up their turn (or multiple turns) / save a juice stockpile, and use it to cancel out the remaining action/juice/move of an opposing unit. In this case, the "PLACE: GOBWIN KNOB" stole the turn of the capital city. Here is some speculation based upon the aforewiki'd speculation:
--Forcibly ending the turn of a King/Overlord automatically ends the turn of the side, similar to how as a general rule units disband when their King/Overlord disbands. Therefore a Turnamancer would only have to *directly* end the turn of one unit (or hex) in order to end the entire side's turn.
--A benefit of the Charlie-powered super-rocketfuel link-up may be to allow Vanna to store up more Turnamancy turns/juice than a turnamancer's "stock" might normally hold, allowing her to expend it in a big burst like this/at such great range like this.
--This ability *is* of extremely specific utility, since the casting restrictions mean this could only be used as a defensive measure on not-the-Turnamancer's-turn while she is either being a) attacked or b) visited by an enemy unit in a friendly/allied city
--Being able to use this at range can only be done with the above condition being fulfilled to 'transmit' the Turnamancy 'attack' through, similar to how Vaarsuvius used to dragon's head as a focus in the Familicide spell
I expect Parson & co. will begin to piece together the conditions necessary to accomplish this gimmick over the next few turns, and they might even be in line with my chain of reasoning here. But I certainly wouldn't expect a trick like this to work regularly - or even have been seen before - because it would necessitate having an enemy King proximate to an enemy Turnamancer on the King's turn while in the Turnamancer's hex/city. As Slately said, Jillian's conduct is quite unseemly - side leaders *rarely* leave their capitals due to the extreme risk their vulnerability levies on their side.