It could be a sort of "split-aspect" spell like what the Pandaren hero uses in Warcraft III's expansion set. For those who haven't played the game, it allows the character to divide its essence up into three smaller creatures, each with a different elemental aspect (one is Fire, another is Air, and the last is Water, if memory serves- I haven't played in a while), and you control the three separately while it lasts. If any of the three survives by the end, the original hero character "recombines" when the effect expires.
OTOH, it could just be a pair of Simulacrum spells and the real Xykon is controlling them through the pendants. Nothing about Simulacrum says the creature to be duplicated has to be living. I'd say the real Xykon is the one currently with Redcloak, in this case, since that's the one that showed the usual sarcasm and disdain for the opposition that we've come to expect from old skull-face over the years.
OTOH, it could just be a pair of Simulacrum spells and the real Xykon is controlling them through the pendants. Nothing about Simulacrum says the creature to be duplicated has to be living. I'd say the real Xykon is the one currently with Redcloak, in this case, since that's the one that showed the usual sarcasm and disdain for the opposition that we've come to expect from old skull-face over the years.