I came here intending to speak based on the Sun teams I've been playing around with, trying to learn from. It looks like reachzero beat me to my main point though, that the Lati@s are the biggest problems to Sun teams overall. Heatran is something that there are already answers for, as well as Rain teams. None of the best counters for the Lati@s fit well onto Sun teams however. Tyranitar is right out, and Steels other than Heatran and maybe Forretress tend to be liabilities, stacking a Fire weakness with Chlorophyll sweepers. Walls like Blissey and Chansey find no place on most Sun teams, because there is no room to fit them. Scarfed or fast Dragons are sometimes seen on Sun, but they compound the Ice Shard vulnerability inherent in Chlorophyll sweepers. Ice types are also hard to fit on Sun, as most of them are bad. Mamoswine is the only reasonable choice, but adds another weakness to Water on a team that has at least one, often two, already. Therefore, something that threatens the Lati@s, while not compounding weaknesses commonly found on Sun teams would be good. As reachzero said, a Dark type is ideal for this.
And building on what others have said, Electric type is also good for this Pokemon. One reason for this is that it threatens Water-types, without gaining a weakness to common coverage moves on the same (Ice Beam). Electric type also gives it some valuble resistances for Sun. A Flying resistance gives Sun a better switchin to Tornadus, and an Electric resistance gives it a switchin to Thunders and Thunderbolts, without risking a Chlorophyll sweeper being paralyzed. Electric STAB also has the advantage of hitting one of Sun's biggest nemeses, Heatran, for Neutral damage.
Therefore, I agree with Dark/Electric as the typing for this CAP. This would give Sun a much-needed answer to the Lati@s, while also being good against Rain, and useful against Heatran.
Ghost/Electric also has its merits, trading some of its effectiveness against the Lati@s for Fighting immunity and spinblocking ability, with the latter of which being useful on a team that often depends on having the hazards advantage.
EDIT: Triple ninja'd!
You just went and posted the most hellish thing I have ever seen in the history of Pokemon, right behind Swagger+Thunder Wave Sableye in hail.-- BlackLight, speaking of my Gravity Jirachi.