Arceus Dragon's niches are it being an offensively typed check to Ho-Oh, Salamence-Mega, Rayquaza and Kyogre-Primal, and has the ability to revenge kill the Lati@s, thanks to them most frequently running Modest nowadays. The latter two (and its ability not to clash with Primal Kyogre) are the only things that justify its usage over Arceus-Water, and should be taken advantage of. A specially defensive variant of Kyogre-Primal is added, giving me plenty of insurance vs CM Arc forms, Darkrai, Xerneas, Sableye-Mega, etc. etc. Using Arceus-Dragon obviously leaves you quite vulnerable to Fairies first and foremost, and of course, the omni-splashable PDon is added. PDon, aside from its obvious valuable qualities, also lures in the Lati twins, which can be easily double switched into Arceus-Dragon, giving it a free turn to Toxic or, if you see a Ferrothorn/Dialga/Klefki / etc. Steel type, make ANOTHER double. etc. etc. Klefki is added to further solidify defense against Fairies, absorb Toxic, and also provides Spikes, further luring in the Lati twins as well as of course providing decent residual damage. At this point, the team's main weaknesses are Primal Groudon, EKiller and Arceus-Ground. Seeing that my mega slot has not been used up, I can go for Salamence-Mega and Giratina-O... I could go for Sableye-Mega and Skarmory... although I dislike the concept of triple dragon in a Fairy-dominant meta, the former is clearly the superior option of the two.