In Kinda, it seemed like the Mara could only possess one person at a time – moving from Tegan to Aris, for example. Snakedance is able to improve on that, as Tegan/Mara is able to corrupt Lon.
This makes sense – since Tegan spends the story possessed by the Mara she requires a confederate to talk to (she could spend it soliloquising but that would probably get somewhat tiresome rather quickly). The fact that Lon is a man of status doesn’t hurt though – this means he would be able to open doors that are closed to others.
Martin Clunes’ performance is often seen as something of an embarrassment, but there’s no reason why it should be regarded as so. Lon isn’t as deep a character as, say, Hindle, but Clunes doesn’t disgrace himself.
But it’s John Carson who really impresses. This episode has one of my favourite Snakedance moments – the six faces of delusion – in which the Doctor manages to demolish Ambril’s superiority with almost indifferent ease. True, it’s hard to believe that Ambril would never have considered the possibility that the ceremonial headdress which features five carved faces would only display six when worn, but given Ambril’s intractability, maybe it’s not too unreasonable after all.
The Doctor continues to be a thorn in Ambril’s side, but since the Doctor is babbling on about death and destruction it’s possibly not surprising that nobody (except young Chela) takes him seriously. But it is rather refreshing that we’re halfway through the story and still the Doctor is positioned as an outsider. This isn’t unique (it’s very late in the day during Frontier in Space before anybody listens to him) but usually by now he’s managed to convince someone of his bona-fides. The early run of the new series, with its psychic paper, made this even less of a problem, but Snakdance takes us back to a time when the Doctor couldn’t simply stroll into any situation and simply take control.