(Click sprites for sets)
Looking at the team so far, I think the way to close it out is with both hazards which it lacks, and a much sturdier check to the primals. Yveltal doesn't exactly appreciate any pdon variant with its set, and Pogre has 0 reliable switch ins currently. I feel like since 3 Arceus is a bit excessive on the roles they share, Zygarde-C is the best choice as a Pdon check. It's one of the sturdiest physical walls in the whole meta if not the bulkiest, and is able to take on most Pdon variants while providing additional defensive support against things like CB Rayquaza, although not a guaranteed fix for that because of Dragon coverage possibilities and how hard it hits, but it helps alleviate the pressure off Arceus-Fairy for that.
Ferrothorn is the Pogre switch in, and as to not double up on Ground-types it was chosen over Pdon, and it gives good support itself that is fairly helpful. Spikes gives much needed hazard pressure to the team, while Leech Seed is always good for chipping things down. Power Whip is chosen as the attacking move to hit Pogre harder since Poisonceus already beats Xerneas, so I think defensively these two round out the team quite well to support Specs Lunala and CM ReRe fairyceus.